The job
Modelled, not recorded. Every figure on this page is re-run through the calculator it names whenever the site is built; the estimate is worked, but no job was carried out, so the last section gives the mechanism of each likely error rather than a measured overrun.
This walkthrough takes one ordinary job and shows the whole takeoff in the order it is actually done, rather than presenting a finished list of quantities with no account of where they came from.
The room is 3 × 4 m with a 2.4 m ceiling, stripped back to the studs. New boarding, a tanked wet area, tiled floor and tiled walls to full height in the shower and to half height elsewhere. One door, one window, and the sanitaryware positions already fixed by the existing drainage.
THE ORDER MATTERS MORE THAN THE ARITHMETIC. Nearly every step needs something from the step before it, and doing them in the wrong order is what produces a bill of materials that looks complete and is short in two places. The tile layout has to be set out before the cut waste can be estimated; the cut waste changes the tile quantity; the tile quantity and the substrate together set the adhesive; and the adhesive coverage depends on the notch size, which depends on the tile format.
WHAT THIS PAGE IS. Every quantity here is computed by the calculators linked at each step, and every waste factor is one this site publishes with its source. It is a modelled walkthrough, not a record of a job that was carried out — so the last section is about where this estimate is most likely to be wrong and in which direction, which is a statement about mechanism rather than a measured overrun. That distinction is stated plainly because the difference between the two is the whole reason a worked example is worth reading.
What was measured, and how
Room dimensions at floor level
3.00 m × 4.00 m nominal, with up to 15 mm variation across each run
Measured wall to wall in both directions at the floor, then again at about a metre up. Rooms are not square and walls are not plumb; the larger figure governs the tile setting out and the smaller one governs whether a full tile fits.
Wall heights, taken at both ends of each wall
2.40 m nominal
Floor to ceiling at each corner. A single central measurement hides a sloping ceiling, which is what makes the top course of tiles taper visibly.
Openings, measured to the structural opening
Door 0.90 × 2.05 m, window 0.60 × 0.90 m
Door and window measured to the opening rather than to the frame, because the boarding runs to the opening and the tiling stops at the frame. Two different figures, and using one for both is a common shortfall.
Wet area extent
Enclosure 0.90 × 0.90 m, tanked to full height plus the specified lap
The shower enclosure footprint plus the required tanking overlap up the adjoining walls and out across the floor. This is the figure that decides the membrane quantity, and it is larger than the enclosure.
Tile format and the layout's starting point
600 × 300 mm floor, 300 × 100 mm brick-bond walls
Chosen before anything is quantified, because the format and the starting line determine where the cuts fall and therefore how much waste there is. A layout set out from a wall and one set out from the room's centre line produce different tile counts.
The takeoff, in order
Each step needs something from the one before it, which is why the order is part of the answer.
Compare tile formats before choosing one
- Needs
- The room dimensions and the candidate tile formats from the measurements above.
- Produces
- A tile count for each format at the waste allowance you set, which makes 600 × 300 against 300 × 300 a comparison of numbers rather than of impressions. It does not place the cuts: where they fall is set out on the floor with a gauge rod, and a slim cut at the doorway is the cue to move the start line before anything is ordered.
Quantify the floor tiles in the chosen format
- Needs
- The floor area and the layout, because the cut pattern rather than the area alone decides how many tiles are consumed. Here that is the whole 3.00 × 4.00 m floor, 12 m² (129 sq ft), in 600 × 300 mm tiles laid straight, with nothing deducted for the enclosure because its floor is tiled inside the tanking rather than taken by a tray.
- Produces
- The tile count: 66.7 tiles of face before any allowance, and 74 once the calculator's straight-lay waste is on — the figure the next step tests against the layout actually chosen.
Result74 tiles, 600 × 300 mm (about 24 × 12 in), laid straight over 12 m² (129 sq ft)
Floor & Wall Tile CalculatorAdd cut waste for the layout actually chosen
- Needs
- The layout's angle and the room's proportions from the first step: the 14 m (45.9 ft) perimeter of the 3 × 4 m floor, and the tile's long side, 600 mm, because the calculator assumes a square tile and its help says to enter a rectangle's long side. That is the lower reading: entered at the short side, the same perimeter gives 47 cut positions.
- Produces
- The waste allowance, which is materially higher for a diagonal or offset layout than for a straight one — the reason this is its own step rather than a flat percentage. Laid straight, as modelled, the allowance is the one already inside step two's 74; laid on the diagonal, the calculator puts a corner cut at 24 perimeter positions and adds 2.16 m² (23.3 sq ft), twelve tiles, to step two's 66.7 of face rather than to its 74: 79 in all, the count step two's calculator gives for a diagonal pattern.
Result2.16 m² (23.3 sq ft) of extra cut waste if the floor went diagonal: 24 corner cuts, twelve tiles
Diagonal Tile Layout 45° Corner Cut Waste CalculatorQuantify the backer board for floor and wet walls
- Needs
- The floor area, the wet-area wall extent, and the openings deducted to the structural opening. The floor is step two's 12 m² (129 sq ft); the enclosure, taken as a corner one, has two room walls boarded to full height, 2 × 0.90 × 2.40 m = 4.32 m² (46.5 sq ft); and neither area has an opening in it.
- Produces
- The board count and the fixings, and the substrate thickness that the tanking and the adhesive both depend on. On 16.3 m² (176 sq ft) at the calculator's bathroom cutting allowance of 15%, that is twenty 1200 × 800 mm boards, about 338 screws and 64 m (210 ft) of alkali-resistant mesh tape.
Result20 boards of 1200 × 800 mm (47 × 31.5 in) for 16.3 m² (176 sq ft) of floor and shower wall
Tile Backer Board CalculatorQuantify the tanking membrane
- Needs
- The wet area extent INCLUDING the laps, not the enclosure footprint.
- Produces
- The membrane area and the roll count, plus the corner and joint treatment, which is where wet-area failures actually happen.
Quantify the adhesive
- Needs
- The tile area from the earlier steps, the tile format, and the substrate — all three, because coverage depends on the notch size and the notch size depends on the format and the flatness. For the floor that is step two's 12 m² (129 sq ft) of 600 × 300 mm tile on step four's board, which the notch table puts at a 10 mm (3/8 in) square notch.
- Produces
- The adhesive quantity, which is the single line most likely to be short. The floor bed alone is 60 kg (132 lb), three 20 kg bags with nothing spare in the last; back-buttered, it becomes 78 kg (172 lb) and a fourth bag. The 300 × 100 mm wall tile takes a smaller notch and is not in this figure.
Result3 bags of 20 kg (44 lb): 60 kg (132 lb) for the floor at a 10 mm notch
Thinset & Tile Adhesive CalculatorQuantify the grout
- Needs
- The tile format, the joint width and the tile thickness — the joint volume is the product of all three, so a change of format changes grout even at the same area. Modelled on the floor: step two's 12 m² (129 sq ft) of 600 × 300 mm tile at a 3 mm (1/8 in) joint filled 8 mm (5/16 in) deep — the calculator's starting values, kept because neither the joint nor the tile thickness is among the measurements.
- Produces
- The grout quantity by weight, which is the one line on this page that rarely moves — joint volume is geometry, so a generous contingency here is padding rather than allowance. At this format under 1.5% of the floor is joint, so the floor takes 2.28 kg (5.0 lb) with nothing added: one 5 kg (11 lb) bag.
Result2.28 kg (5.0 lb) of grout for the floor, with no allowance added
Grout CalculatorQuantify the trims and the spacers
- Needs
- The tiled extents from the layout, and where tiling stops against a non-tiled surface. With the enclosure in a corner, that is the top of the half-height tiling along the other 11.3 m (37.1 ft) of wall — the 14 m perimeter less the enclosure's two walls and the doorway — the two vertical ends of the full-height tiling above it, 1.2 m (3 ft 11 in) each, and the 0.90 m (2 ft 11 in) threshold: 14.6 m (47.9 ft).
- Produces
- The trim lengths, which are routinely forgotten at the takeoff and bought twice at retail prices. With the calculator's allowance for mitres and offcuts that is 15.8 m (51.7 ft), rounded up to whole lengths of whatever profile is chosen. The window reveal is not in it: its sill height was not measured, and only a sill below the tiling line brings the reveal into the tiled area.
Result15.8 m (51.7 ft) of edge profile from 14.6 m (47.9 ft) of exposed edge
Tile Edge Profile (Trim Strip) Linear Footage CalculatorQuantify the plasterboard for the dry walls and the ceiling
- Needs
- The wall and ceiling areas not taken by backer board, with the openings deducted. The wall calculator takes the room as measured — 3.00 × 4.00 m at 2.40 m — and deducts the door and window at their structural openings, 0.90 × 2.05 m and 0.60 × 0.90 m.
- Produces
- The board count and the jointing materials for the areas that are decorated rather than tiled. For all four walls that is 31.2 m² (336 sq ft) net and twelve 2400 × 1200 mm sheets at the calculator's 10% — an upper bound for the walls, because the enclosure's 4.32 m² (46.5 sq ft) inside it is step four's backer board. The 12 m² (129 sq ft) ceiling is a separate area this figure does not include.
Result12 sheets of 2400 × 1200 mm (12 of 8 × 4 ft) over 31.2 m² (336 sq ft) of net wall
Drywall Calculator
The figures
| Step | Calculator | Figure |
|---|---|---|
| Quantify the floor tiles in the chosen format | Floor & Wall Tile Calculator | 74 tiles, 600 × 300 mm (about 24 × 12 in), laid straight over 12 m² (129 sq ft) |
| Add cut waste for the layout actually chosen | Diagonal Tile Layout 45° Corner Cut Waste Calculator | 2.16 m² (23.3 sq ft) of extra cut waste if the floor went diagonal: 24 corner cuts, twelve tiles |
| Quantify the backer board for floor and wet walls | Tile Backer Board Calculator | 20 boards of 1200 × 800 mm (47 × 31.5 in) for 16.3 m² (176 sq ft) of floor and shower wall |
| Quantify the adhesive | Thinset & Tile Adhesive Calculator | 3 bags of 20 kg (44 lb): 60 kg (132 lb) for the floor at a 10 mm notch |
| Quantify the grout | Grout Calculator | 2.28 kg (5.0 lb) of grout for the floor, with no allowance added |
| Quantify the trims and the spacers | Tile Edge Profile (Trim Strip) Linear Footage Calculator | 15.8 m (51.7 ft) of edge profile from 14.6 m (47.9 ft) of exposed edge |
| Quantify the plasterboard for the dry walls and the ceiling | Drywall Calculator | 12 sheets of 2400 × 1200 mm (12 of 8 × 4 ft) over 31.2 m² (336 sq ft) of net wall |
The waste factors, and why these ends of the ranges
| Material | Applied | Why |
|---|---|---|
| Floor tiles | The upper end of the published range for this layout | A 600 × 300 tile in a room with 15 mm of variation across each run produces tapered cuts on two edges, and a large-format cut that goes wrong is a whole tile rather than a corner. The lower end of the range assumes a square room and a small format. |
| Wall tiles | The middle of the range, raised at the internal corners | A brick bond on a small format is forgiving, and the cut pieces from one course are usable in the next. The corners are the exception, because a cut that has to be both square and the right width usually is not. |
| Adhesive | The upper end, and stated as a range rather than a figure | Coverage moves more with the SUBSTRATE than with the tile. A flat board takes the notch's nominal bed; a wall that needs building out takes considerably more, and back-buttering a large format raises it again. This is the line where a single number is least defensible. |
| Grout | The published rate, with no addition | Grout volume is geometry — joint width times depth times length — and it varies far less than adhesive. Adding a large contingency here is padding rather than allowance. |
| Backer board and plasterboard | Standard sheet-goods allowance, rounded up to whole boards | The real constraint is that boards come in fixed sizes, so the rounding dominates the percentage. A room a little over a board module costs a whole extra board whatever allowance is applied. |
Where this estimate is most likely to be wrong
Adhesive
usually overThe estimate assumes a flat substrate and the nominal bed for the notch size. Real walls are rarely flat, and the adhesive takes up the difference — so consumption rises with how much the wall has to be built out, which is not known until the boarding is up. Back-buttering large-format tiles, which is often necessary rather than optional, raises it again.
Narrow it by: Checking the substrate with a straightedge before ordering, and deciding then whether the tiles will be back-buttered.
Floor tiles
usually overCut waste depends on where the cuts land, which depends on the setting out. A layout that puts a narrow strip along one wall wastes most of each tile in that row, and large formats amplify it because a spoiled cut costs a whole tile.
Narrow it by: Running the layout calculator with the actual room dimensions before ordering rather than applying a flat percentage to the area.
Tanking membrane
usually underThe laps and the corner treatment consume more than the enclosure's area suggests, and the extent tanked on site is often larger than the extent drawn — because whoever is applying it extends it to the nearest sensible stopping point rather than to a dimension.
Narrow it by: Quantifying from the tanked extent including laps rather than from the shower footprint.
Trims and profiles
usually underTrim lengths are taken off last and are the item most often missed entirely, and they are sold in fixed lengths — so a run a little over a length costs a whole extra one, and the offcut is rarely usable elsewhere.
Narrow it by: Listing every edge where tiling stops against something else before ordering, including reveals and the top of half-height tiling.
Plasterboard
either waySheet-goods rounding dominates. Whether the room's dimensions fall just over or just under a board module changes the count by a whole board in either direction, and the openings' deduction is only worth taking where a full board is saved by it.
Narrow it by: Laying the board modules out against the actual wall lengths rather than dividing area by board area.
Tools this job needs
Frequently asked questions
- How many tiles do I need for a 3 × 4 m bathroom floor?
- In 600 × 300 mm (about 24 × 12 in) tiles laid straight, the 12 m² (129 sq ft) floor is 66.7 tiles of face and 74 once the straight-lay allowance is added. Laid on the diagonal, the corner cuts at 24 positions round the 14 m (45.9 ft) perimeter add 2.16 m² (23.3 sq ft), twelve tiles, to the 66.7 of face: 79 in all. Where the setting out starts moves where the cuts fall, which is why the layout is fixed before the order.
- How much tile adhesive and grout does a bathroom floor need?
- For 12 m² (129 sq ft) of 600 × 300 mm tile on backer board, a 10 mm (3/8 in) square notch lays about 60 kg (132 lb) of adhesive: three 20 kg (44 lb) bags with nothing left in the last one. Back-buttering, often needed at this format, raises it to 78 kg (172 lb) and four bags. Grout is smaller and steadier — 2.28 kg (5.0 lb) at a 3 mm (1/8 in) joint 8 mm (5/16 in) deep, one 5 kg (11 lb) bag.
- How many backer boards does a bathroom floor and shower need?
- Here the board covers the 12 m² (129 sq ft) floor and the two room walls of a 0.90 m (2 ft 11 in) square corner enclosure to full height, 4.32 m² (46.5 sq ft): 16.3 m² (176 sq ft) in all. In 1200 × 800 mm (47 × 31.5 in) boards with a 15% bathroom cutting allowance that is 20 boards, fixed with about 338 screws and taped with 64 m (210 ft) of alkali-resistant mesh. The remaining walls and the ceiling take plasterboard.