Three at the Top, Nine at the Bottom
The old leaf comes off in a minute and takes the argument with it. What is left is a softwood lining fitted when the house was built, plastered against on both faces, painted eleven times, and quietly working ever since: the head has taken a small sag where the trimmer above it dried out, the hinge jamb has bowed toward the room, and the latch jamb leans. Hold a straightedge on the closed face of the lining and the gap under it tells you the whole story. Offer the new leaf up on a pair of wedges and the story becomes arithmetic — three millimetres of margin at the top of the lock stile, nine at the bottom, and a leaf that will not close at all until something comes off somewhere.
That is the actual job. Not fitting a door: reconciling a rectangle bought to the nearest millimetre with an opening that stopped being rectangular before most of us were born. Every decision from here is a decision about where to spend the discrepancy — how much off each stile, how much off the head, how much left at the bottom for a floor covering that has not been chosen yet, and how much of the remainder gets hidden behind architrave rather than cut away at all.
The order matters more than the technique. Measure and mark everything before the plane comes out, because a stile you have taken 6 mm off cannot give any back, and the sequence that gets a leaf hung and latched in one go is: read the opening, decide the whole reduction, split it across the edges, cut the recesses in both the leaf and the lining, hang on the top hinge alone, then plant the stops and mark the keep off the latch itself. Reverse any two of those and you will be taking the door down again.
Survey the Hole, Not the Door That Was In It
The temptation is to use the old leaf as a template. Resist it — the old leaf was itself scribed to this lining by somebody working around a different set of problems, it has been trimmed at the bottom for a carpet that went out in 1991, and its hinge positions were chosen for 75 mm butts nobody stocks in the same knuckle pattern any more. Copying it copies the compromises without the reasoning. Measure the opening cold, in its own right, and treat the old door as scrap timber with useful screws in it.
Five measurements settle most of it, and the fifth is the one that surprises people. Width at the head, width at the middle, width at the floor; height on both stiles; and then the twist. Hold a spirit level flat against the hinge jamb face and against the latch jamb face in turn — if one reads plumb and the other leans, the lining is in wind, and a flat leaf closed into it will touch high on one side and low on the other. On an internal lining that is a recoverable fault, because the stop is planted rather than rebated: you hang the leaf first and then set the stop to where the leaf actually sits, which absorbs the twist invisibly. In a rebated frame the same fault is a packing job or a compromise.
- Strip the old leaf and hinges, and pull every screw and pin out of the lining rather than working around them.
- Take width at head, mid-height and floor, and height at both stiles; work to the tightest of each pair.
- Check both jamb faces for plumb and for wind, and note which corner runs out.
- Straightedge the closing face of each jamb and the head, and note any bow toward or away from the room.
- Check the floor across the opening for level and for hump, since a door binds on a raised board long before it binds on a jamb.
- Fill or glue timber into the old hinge recesses now, so the new marking-out has sound material under it.
What is actually in a door opening
- Architrave, mitred at both head corners — covers the joint between lining and plaster, and is bought in whole sticks long enough to run a leg without a seam Door & Window Casing Calculator
- The leaf, on three butt hinges — the only rectangular thing in the assembly, and the only piece that arrives without knowing what the opening did for fifty years Timber Cross-Grain Shrinkage Calculator
- Lining, with the stop planted on afterwards — sets the plumb the leaf hangs to, and its planted stop is what lets a twisted opening still close tight
- Packers at every fixing point — hold the lining straight against the fixing screw instead of letting it draw in and bow toward the room Timber Fastener Withdrawal Capacity Calculator
- Studwork or masonry opening — trimmer studs under a header, or a masonry reveal — whatever the builder left, out of square by whatever it has moved since, and not adjustable at this stage
What the Leaf Will Let You Take
How much can come off is decided by what is behind the edge, and on a modern leaf that is rarely solid timber all the way through. A hollow-core flush door is a perimeter of framing with a lipping over it, a paper or timber lattice core, and a lock block glued in on one stile at handle height. Take too much off the lock stile and the mortice for the latch ends up in the void beside the block; take too much off the hinge stile and the middle hinge screw finds cardboard. Neither failure announces itself until the hardware goes in, which is after the leaf has been planed, sealed and offered up.
Engineered and solid-core leaves are more forgiving but not unlimited, and the limit is a published one rather than a matter of judgement. For architectural flush doors, WDMA I.S.1A, Architectural Wood Flush Doors, is the industry standard the manufacturer builds to and the place trimming allowances are stated; European and UK joinery is covered by BS EN 942, Timber in joinery — General requirements, with internal doorsets sitting under BS EN 14351-2, Windows and doors — Product standard, performance characteristics — Part 2: Internal pedestrian doorsets. In every case the door supplier's own literature carries the number that applies to the door in front of you, and it is worth having that sheet on the bench before the first shaving.
Split the reduction rather than spending it in one place. If the opening is 14 mm narrower than the leaf, taking 7 mm off each stile keeps the lock block roughly under the latch and keeps enough width under the hinge screws, where taking the whole 14 mm off one edge may do neither. The exception is a leaf that has to be scribed to a jamb that is out of line: there the shape of the cut is set by the jamb, and the arithmetic only decides the total. Set a pair of dividers to the widest gap, run them down the jamb with the leaf wedged at an even head margin, and cut to the line — a tapered stile that follows the lining reads as a perfect fit, while a parallel stile in a tapered opening reads as a mistake at both ends.
Fire doors are a different question and should be treated as one. A leaf tested to BS EN 1634-1 or BS 476-22 was tested as a complete assembly — leaf, frame, intumescent seals, hinges, latch and closer together — so a fire-rated leaf hung into an existing 1974 lining is not a fire doorset, whatever the label on the leaf says. BS 8214, Timber-based fire door assemblies — Code of practice, covers installation and the gap tolerances the assembly was tested at; British Woodworking Federation Fire Door Alliance literature covers the certification schedules in the UK; and in North America NFPA 80, Standard for Fire Doors and Other Opening Protectives, governs both the clearances and which field modifications are permitted at all. Where Approved Document B requires a fire door — a loft conversion stair, a door between a dwelling and an integral garage — the honest answer is usually a complete certified doorset rather than a leaf and a hope.
| Edge | What is behind it | What sets the limit |
|---|---|---|
| Hinge stile | A solid stile, or a lipping over a framed perimeter, carrying the whole weight of the leaf through the hinge screws | The width of sound material left under the screw, and the trim allowance in the manufacturer's literature |
| Lock stile | The lipping, and on a flush leaf a lock block of limited length glued in at handle height | Where the lock block starts and stops — a mortice past its edge is a mortice in the core |
| Top rail | Usually the narrowest framing member in the leaf | The maker's stated allowance; on a fire door, the certification schedule for that leaf |
| Bottom rail | Often deeper than the top rail, and the edge most likely to be cut on site | The finished floor build-up, any undercut required for return air, and the maker's allowance |
| All four edges | Exposed end and side grain once cut, on a leaf that was factory-sealed only on its faces | Nothing dimensional — but an unsealed cut edge takes up moisture and undoes the fit |
The Gap Has to Survive February
A margin that reads perfectly on the day is a margin measured at one moisture content. Timber moves across the grain as it takes up and gives off water, and a leaf hung in a house that is still drying out from plastering will be a different width by the time the heating has run a full winter. The direction is the part people get backwards. A leaf fitted damp — delivered in the rain, stored in an unheated garage, hung into a room that has just been skimmed — dries in a heated house and the gaps grow: the latch gets sloppy, the door rattles in its stop and the room stops being private. A leaf fitted bone dry out of a warm room swells when the house is unheated and humid, and binds on the lock stile in the first wet August.
The useful thing to know is that a framed leaf moves far less than its own width suggests, and that is the whole point of framing it. A one-piece board 762 mm wide, drying from the high teens to the high single figures, would lose over a centimetre across its width — enough to open a gap you could post a letter through. A panelled or engineered leaf of the same width moves only by the summed width of its cross-grain members, because the panels float in their grooves and the rails run with the grain along the width. Two stiles of around 95 mm are 190 mm of cross-grain timber, not 762 mm, and the movement scales with that. Enter the stile widths rather than the leaf width and the answer stops being alarming and starts being a gap you can actually design.
Which leaves the practical instruction, and it is the cheapest one in the trade: bring the leaves into the room they will live in, lay them flat on bearers with sticks between them so air gets to both faces, and leave them there for several days before cutting anything. Conditioning the leaf to the room removes most of the movement from the equation before you have committed a single millimetre. Where that is not possible — a handover next week, a house with no heating on yet — take a meter reading, work out which way the leaf will go and by how much, and bias the margins accordingly: slightly generous on the lock stile if the leaf is dry and the house will be damp, slightly tight if it is the other way round.
Run it with the summed width of the leaf's cross-grain members rather than the leaf width, and the level count set to one — the calculator is written for a stacked frame but its single-member case is exactly this. A negative answer means the leaf is going to grow, not shrink, which tells you which edge to be generous on.
The summed depth of horizontally laid timber the load path passes through at one level.
The meter reading taken on the timber at the moment it was fixed in place.
Where the timber will settle once the building is finished and running.
The fraction of its depth the timber moves for each single point of moisture change.
How many platform-framed levels the movement accumulates through.
Cross-grain movement at one floor level
0.2749 in
Straight arithmetic on the coefficient and the moisture change entered. The movement is across the grain; along the grain the same change moves the timber by a small fraction of this and is normally ignored.
- Accumulated movement over all floor levels
- 0.82 in
- Depth remaining once the movement has happened
- 11.48 in
- Movement for a single point of moisture change
- 0.03 in
- Change in moisture content
- 9 %
- Proportion of the depth lost
- 2.34 %
They open the calculator with your figures already in it
Timber Cross-Grain Shrinkage Calculator: 0.2749 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 0.2749 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Movement across the grain only. Timber moves along the grain by a small fraction of this, and a long member's length is effectively stable.
- Says nothing about whether the movement will be RESTRAINED. A member free to shrink simply shrinks; the split the guide describes happens when two rigid fixing lines hold a deep section apart while it tries to move, and that is a detailing question this arithmetic cannot answer.
- Uses one coefficient for the whole stack. Where the plates, the rim and the joists are different species or different sawing patterns, run them separately and add the results.
- Ignores creep, mechano-sorptive movement under sustained load, and any moisture cycling. A detail that dries, wets and dries again does not simply return to where it started.
Butts, Positions and What Actually Holds Them
Three hinges on an internal leaf is the sensible default even where two would carry it, because the third one stops a leaf bowing and keeps the lock stile parallel to the jamb over time. The conventional layout puts the top hinge about 150 mm down from the top of the leaf, the bottom hinge about 225 mm up from the bottom, and the third either centred between them or set close under the top hinge on a heavy or wide leaf, where the load it is sharing is the load that matters. Those are trade conventions rather than clauses, and the one that is not negotiable is that the hinge positions on the leaf and the recesses in the lining are marked from a single common datum — usually the head margin — rather than measured separately from each part.
Hinge selection has a published route. BS EN 1935, Building hardware — Single-axis hinges — Requirements and test methods, grades hinges by a classification that includes the door mass and the duty cycle they were tested at; ANSI/BHMA A156.1, Butts and Hinges, is the equivalent in North America. Both let you choose on evidence rather than on the weight of the box, which matters on a solid-core or fire-rated leaf, where the mass is well beyond what a light pressed butt was tested to carry. On a fire door the number of hinges and their grade are part of the certification schedule and are not a site decision at all.
The recesses are where a hung door is won or lost. Cut them so the hinge leaf sits dead flush with the timber — too deep and the knuckle is pinched as the door closes, which is hinge-bound: the leaf springs back off the stop and refuses to latch. Too shallow, with the hinge standing proud, and the extra thickness pushes the leaf across the opening until it drags on the lock stile with the margin there closed to nothing. If a hung door springs open by a few millimetres and the latch will not hold, take the middle hinge screws out before touching the latch, because hinge-bound is the fault that most often gets mistaken for a keep in the wrong place. A slip of card behind the offending hinge leaf is the classic cure and it is a legitimate one.
Screws are the quiet failure, particularly in a lining that is a half-century of softwood with old fixings pulled out of it. The whole weight of the leaf is levering the top hinge out of the jamb, which is a withdrawal load, and withdrawal in timber is a function of the fastener diameter, how deep it penetrates and how dense the receiving material is. Short screws into a bowed lining that is not packed behind will loosen: the lining flexes, the screw works, and six months later the door is catching at the head. Pack behind the lining at every hinge, drill clearance and pilot properly, and use at least one screw per hinge long enough to reach past the lining into the stud or the plugged reveal behind it.
- Wedge the leaf into the opening at the final head margin and mark all three hinge positions across leaf and lining in one pass.
- Square the marks onto both edges, gauge the width and the depth from the hinge itself, and cut the leaf recesses first.
- Cut the lining recesses to the same datum, checking there is sound timber behind each one after the old ones were filled.
- Fix the hinges to the leaf, then hang on the top hinge only with a single screw and let the door tell you what it wants.
- Add the remaining hinges and screws, then check the margins all round before the last screw is driven.
- Plant the stops to the closed leaf, not to a mark on the lining, so any twist in the opening is taken out here.
The top hinge is being pulled straight out of the jamb by the weight of the leaf. Run the screw diameter, the penetration you actually get past the lining and the density of what it lands in, and the case for a longer screw into the stud behind makes itself.
Which fastener is resisting the pull, because each has its own published equation.
The unthreaded shank diameter of the fastener, not the diameter over the thread.
How far the fastener actually enters the member that has to hold it.
The assigned specific gravity of the species the fastener bites into.
Whether the fastener enters across the fibres or straight into the cut end.
The moisture adjustment your own code table gives for this fastener and this exposure.
How many fasteners share the pull at this one connection.
Withdrawal capacity of the group
6.811 kips
Side grain, dry service, and the published reference equation for this fastener applied directly. This is a reference design value: the load duration factor and any temperature factor still have to be applied on top of it.
- Withdrawal capacity of one fastener
- 1,135.21 lbf
- Withdrawal resistance per unit of penetration
- 4,540.84 lbf/ft
- Fasteners in the group
- 6 fasteners
- Combined reduction applied for grain direction and moisture
- 1 factor
They open the calculator with your figures already in it
Timber Fastener Withdrawal Capacity Calculator: 6.81 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 6.811 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Applies the moisture and end-grain adjustments only. The load duration factor CD, the temperature factor Ct and the toe-nail factor are separate multipliers this page does not apply.
- Reference design values are for smooth-shank fasteners. A ring-shank, screw-shank or proprietary structural screw withdraws considerably better, and its capacity comes from the manufacturer's evaluation report, not from these equations.
- Says nothing about head pull-through, about the side member splitting, or about the fastener's lateral capacity — a hold-down usually fails at one of those before the shank ever pulls out of the timber.
- A rated strap, hanger or hold-down is designed on its own tested capacity with every specified hole filled. Where such a product is used, this calculation is a cross-check on the fasteners, not a substitute for the rating.
Latch and Keep, First Time
Fit the latch after the leaf is hung, not before. The temptation is to mortice it on the bench while the door is flat and easy to work, but the leaf may still lose a shaving off the lock stile once it is swinging, and a mortice cut to the old edge ends up with the forend proud or buried. Hang first, confirm the margins, then mark the latch — and mark the backset off the door stile with the handle position already decided, since the height band for door handles comes from the adopted access document rather than from habit. In England that is Approved Document M, Access to and use of buildings.
The keep is marked off the latch, never off a tape. Close the leaf until it sits where the stop will be, and mark the top and bottom of the latch bolt onto the face of the lining with a knife. Open the door, square those marks across, and set the backset from the leaf face — the bolt has to enter the keep without the door having to be pushed or lifted to meet it. A drop of paint or a marker on the bolt face, then closing the door hard against the lining, gives you the same information as a print if you prefer to see it rather than measure it. The keep mortice is cut to that print, deep enough that the bolt throws fully, and the plate is let in flush so nothing catches the leaf edge as it swings past.
Where the keep is a fraction out, the direction of the fix is worth knowing before you start filing. A bolt that hits the plate too high or too low is a marking error and the plate moves. A bolt that reaches the plate but will not throw is a depth problem in the mortice behind it. A door that has to be pulled to latch is not a keep problem at all — it is the stop planted too proud, or a hinge-bound leaf pushing back — and filing the keep to cure it only produces a door that rattles once the real fault is found. Test with the handle and with a push, both, before deciding which of the three you have.
Architrave Covers the Difference, Within Reason
Architrave is the last chance to make the opening look intentional, and it works because it spans the joint between a lining that is straight and a plaster face that is not. Set an even margin back from the lining edge on all three legs — a consistent reveal is what the eye reads as square, far more than the actual geometry does — and scribe the outer edge to the wall where the plaster falls away, rather than pinning the architrave flat and leaving a shadow gap that runs out along its length. Mitres open as the lining dries and the fixings settle; glue them and pin through the mitre as well as through the face, and they stay closed.
Buy it by the stick and count the whole house at once. A door is cased on three sides on each face, which is two legs and a head per side, and the leg length is why architrave is stocked at a length that clears a standard door height in one piece — a seam in a leg is visible from across the room for the life of the building. On a refurbishment where every door is being changed, the count runs well past what anyone holds in their head, and running two sticks short on the last opening means either a second delivery or a different batch with a slightly different profile.
It counts one opening per FACE, not one per door — two legs and a head is what it prices, so a door cased on both sides is two openings in the count and a whole house is twice the door schedule. The mitre waste is already in the figure, and the answer arrives in sticks of the length your supplier actually stocks.
SettingsSettings for this calculation
The standard allowance most suppliers and estimating guides assume for ordinary work.
Doors are cased on both jambs and the head; windows are cased on all four sides.
The height of the rough opening.
The width of the rough opening.
How many identical door or window openings you're casing.
The length casing stock is sold in at your supplier.
Extra casing for mitre offcuts and a recut joint.
Casing needed
17.6 linear ft
- Casing needed (before waste)
- 16 linear ft
- Sticks needed
- 3 x 7 ft sticks
They open the calculator with your figures already in it
Door & Window Casing Calculator: 17.6 linear ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The stick figure is a length division — the run with waste divided by the stock length and rounded up — and it takes no account of which piece has to come out of which stick. A 2.032 m door leg cut from an 8 ft (2.44 m) stick leaves 406 mm, too short for the 864 mm head, so four identical doors take ten sticks on the bench against the nine that division returns. Openings of different sizes have to be run separately and their stick counts added, because offcuts from one run are not pooled into another.
- No casing width is collected, so the run is the bare opening and nothing else. A mitred picture frame round a window adds about eight times the casing width, since each of the four pieces runs past the opening at both ends: 456 mm for a 57 mm profile and 712 mm for an 89 mm one. A door adds about four times the casing width, roughly 0.75 linear ft on a standard opening with a 2 1/4 in architrave, which is already half of the default 10% allowance before a single mitre offcut is cut.
- Rough opening, finished jamb and door leaf are three different heights and the calculator simply uses whichever you type. The 2.032 m default is an 80 in leaf rather than a rough opening, and it is not the leg length either: a leg is cut from the finished floor to the top of the head casing, which with an 89 mm architrave over that leaf sits past 2.13 m and will not come out of a 2.1 m stick at all, even though the total-length arithmetic accepts that stock length without complaint.
- The window option assumes a four-sided picture frame. A window finished with a stool and apron is cased on three sides instead, so the four-sided figure overstates it by one opening width per window — 0.9 m on a 1.2 m by 0.9 m opening — while the stool itself, which runs past the legs by a horn at each end, and the apron beneath it are different sections this page does not produce.
- Plinth blocks and corner rosettes change the geometry the figure assumes: a plinth block takes its own height, commonly 130 to 150 mm, off the foot of each leg, and rosettes remove the mitres so the head is cut square between them rather than long-point to long-point. Extension jambs or a jamb rip, needed wherever the wall finish stands proud of the jamb face, are a separate material in a separate width and are outside this total. The height and width fields stop at 3 m, so a 12 ft (3.66 m) patio slider or a wide bifold opening has to be split across runs.
Six Faces, and Hanging It Twice
Every cut edge has to be sealed, including the top edge nobody can see. A factory-finished leaf is sealed on its faces and often on its edges, and every stroke of the plane removes that seal and exposes fresh timber to whatever the room's humidity is doing. The top edge is the one that gets skipped, because it is out of sight and the door is already hung by the time anyone thinks of it — and it is the edge that sits closest to the warm, moist air collecting at ceiling level. An unsealed top edge is the commonest reason a leaf that fitted in March is binding by August, and it costs one coat and five minutes to prevent.
Plan on hanging the door twice. The first hang is diagnostic: on the top hinge and a single screw, with the leaf swung through its full travel, watching where it touches and whether it drifts open or shut on its own. Take it down, correct what the swing showed you, seal every worked edge, and hang it properly. A door hung once, sealed nowhere and adjusted with the hardware already fitted is a door that will be back on the bench inside a year — and by then the architrave is on, the decorator has been over the lot, and taking it apart costs a great deal more than it did on the day.
Close out with the things that only appear once the room is finished. Operate the leaf through its full arc with the floor covering down, and check the bottom gap against whatever is actually there rather than against the bare boards you fitted to. Confirm the latch engages with a normal push and holds without being pulled. Look along the closed leaf from the side to see that it sits parallel to the lining rather than proud at one corner, which is the last symptom of a lining still in wind. Then write down the leaf sizes and the hinge and latch models you used, because on a house full of doors the second one is a great deal quicker when the first one has been recorded.
Settle these before the plane comes out
Five things that are cheap to decide with the leaf still on the bearers and expensive to discover with it hung.
- The whole reduction, and how it splits across the edges — Tightest width and tightest height, minus the margins you want — then decide how much comes off each stile rather than spending it all on one.
- The trim allowance for this specific leaf — From the manufacturer's literature, and from the certification schedule if it is a fire door. Hollow-core leaves have a lock block and a limit.
- Which way the leaf is going to move, and how far — Summed cross-grain stile width, the moisture it is at now and the moisture it will settle to. Condition the leaves in the room first if there is time.
- Hinge count, grade and screw length — Three butts as a default, graded to the leaf mass, with at least one screw per hinge reaching past the lining into solid material behind.
- Architrave sticks for the whole job — Two legs and a head per face, counted on both faces of every opening on the job, in a stock length that runs a leg without a seam.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.