How do I space balusters evenly between two posts?

Choose a gap at each end, enter the clear distance between the posts, the baluster's face width and the largest gap your code allows, and keep the maximum on the clear gap. The page gives the fewest balusters that keep every gap at or under it, the gap they actually leave, and where each one goes measured from the first post. On an 8 ft (2.44 m) bay of 1.5 in (38 mm) balusters held to 4 in (101.6 mm), that is 17 balusters with gaps of 3.92 in (99.5 mm), marked at 3 15/16 in.

What is the difference between the gap and the centres?

The gap is the clear space between two neighbouring items, face to face; the centres are measured from the middle of one item to the middle of the next. The centres are always one item's width more than the gap. Guard openings are limited as a clear gap; fixings, posts and joists are usually specified at centres.

Should the run start and finish on a post or on a gap?

On a gap when the ends are already fixed, as with balusters between newel posts or battens between two walls: the end posts are not counted and the end spaces equal the others. On an item when the first and last of the things being spaced sit at the ends, as with a line of fence posts or a row of fixings along a rail: those two are counted, and the run is measured over their outside faces.

Why are the marks measured from one end instead of from item to item?

Because every measurement carries a small error, and stepping from one item to the next adds each error to the one before. Measured from a single starting point, each mark carries only its own rounding, so the last space comes out the same as the first. Hook the tape once at the start and mark every figure from it.

Can I use this for stud or joist layout?

Only where nothing has to land on the members. Studs and joists under sheet materials are set at a fixed centre, 16 in or 24 in (406 mm or 610 mm) in North America and 400 mm or 600 mm (15.7 in or 23.6 in) in the UK, so that board edges fall on them, and the last bay is simply short. Equal spacing would move every member off the board joints. The stud calculator lays framing out that way.

How is this different from the deck baluster calculator?

The baluster calculator counts the balusters in one bay against the guard's sphere for your unit system, and gives the gap they leave. This page takes any item and any maximum, gap or centres, starts and finishes the run either way, accepts a count you choose instead, and lists the mark for every item.

Measurements & Conversions

Equal Spacing Calculator (Balusters or Spindles, Posts, Battens)

Space balusters, posts, battens or fixings equally: the fewest that keep every gap or centre under your maximum, and each mark from one end.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Length of the Run

The distance the items are spread across, measured between the faces they start and finish against.

With gaps at both ends, measure the clear distance between the inside faces of the end posts, newels or walls, at the height the gaps will be checked. With items at both ends, measure from the outside face of where the first item will stand to the outside face of the last; for a line of posts known by their centres, add one post's width to the centre-to-centre distance.

Tools needed: Tape measure

Width of Each Item

The face width of one baluster, post, batten or fixing, measured along the run; 0 for marks to points.

Measure the item itself rather than its nominal size: a square spindle sold by its section, a post's actual face, a batten's dressed width. Leave it at 0 for things with no width worth counting, such as screw positions or drill holes, and the marks are simply equal divisions of the run.

How the Run Starts and Finishes

A gap at each end, for balusters between two posts; or an item at each end, for a line of posts or battens.

Balusters, spindles and pickets between two posts start and finish on a gap: the posts are already there and are not counted. A fence line, a row of battens on a wall or a set of fixings along a rail starts and finishes on an item, and those two end items are counted in the answer.

Count

Let the page find the count from a maximum spacing, or give the count and get the spacing.

With a maximum, the page finds the smallest count whose equal spaces all come out at or under it, so the spaces usually land a little under the maximum. With a count of your own, the page shares the run out equally between them, whatever the spaces come to.

The Maximum Applies To

A guard's opening limit is a clear gap; a fixing pitch or a span is usually given as centres.

The two differ by one item's width. An opening limit is measured in the clear, between the faces of neighbouring balusters. Fixing pitches, post spacings and spans are given centre to centre, from the middle of one item to the middle of the next.

Largest Spacing Allowed

The most the gap or centres may be, from your code, the maker's instructions or the design: 100 mm (3.94 in) and 4 in (101.6 mm) are guard-opening limits.

The page opens on a guard's opening limit because that is the commonest case: 100 mm (3.94 in) in metric, the sphere of England's Approved Document K and Canada's National Building Code, and 4 in (101.6 mm) in imperial, the International Residential Code's. Your own code may set another figure, Australia's 125 mm (4.92 in) for one, and that figure governs. For battens, fixings or posts, enter the maximum the product's instructions or the span table give.

Marks To

Where each mark is measured to: the middle of the item, or the edge nearer the start of the run.

Centre marks suit posts and fixings, where the item is centred over the line. Edge marks suit balusters and battens, where the item's edge is held to the line: mark the line, put a cross on the side away from the start, and set the item on the cross.

Items to set out

17 items

High confidence

Every space is the same, the first and last included, and every mark is measured from the start of the run, rounded on its own to the nearest 1/16 in (1.6 mm) in imperial and given exactly in millimetres in metric.

Clear gap between items: 3.92 in (3 15/16 in)
Centre-to-centre spacing: 5.42 in (5 7/16 in)
Equal spaces across the run: 18 spaces
Largest gap allowed: 4 in
Item 1, centre from the start: 4.67 in (4 11/16 in)
Item 2, centre from the start: 10.08 in (10 1/16 in)
Item 3, centre from the start: 15.5 in (1 ft 3 1/2 in)
Item 4, centre from the start: 20.92 in (1 ft 8 15/16 in)
Item 5, centre from the start: 26.33 in (2 ft 2 5/16 in)
Item 6, centre from the start: 31.75 in (2 ft 7 3/4 in)
Item 7, centre from the start: 37.17 in (3 ft 1 3/16 in)
Item 8, centre from the start: 42.58 in (3 ft 6 9/16 in)
Item 9, centre from the start: 48 in (4 ft 0 in)
Item 10, centre from the start: 53.42 in (4 ft 5 7/16 in)
Item 11, centre from the start: 58.83 in (4 ft 10 13/16 in)
Item 12, centre from the start: 64.25 in (5 ft 4 1/4 in)
Item 13, centre from the start: 69.67 in (5 ft 9 11/16 in)
Item 14, centre from the start: 75.08 in (6 ft 3 1/16 in)
Item 15, centre from the start: 80.5 in (6 ft 8 1/2 in)
Item 16, centre from the start: 85.92 in (7 ft 1 15/16 in)
Item 17, centre from the start: 91.33 in (7 ft 7 5/16 in)

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

International Residential Code R312.1.3 — openings in a required guard must not allow passage of a 4 in (101.6 mm) diameter sphere; one example of the maximum a reader enters
Approved Document K (2013 edition), Section 3 — guarding in a building likely to be used by children under five should not have openings that allow passage of a 100 mm (3.94 in) sphere; the metric example
NIST Handbook 44 (2026 edition), Appendix C: 12 inches = 1 foot and 1 inch = 2.54 centimetres exactly, the basis of the tape readings and of the millimetres a metric reader is shown

Inputs used

Length of the Run: 8 ft
Width of Each Item: 1.5 in
How the Run Starts and Finishes: Gap at each end (between posts)
Count: Fewest under a maximum
The Maximum Applies To: The clear gap between items
Largest Spacing Allowed: 4 in
Number of Items: 10
Marks To: The centre of each item

Intermediate steps

Clear gap between items: 3.92 in (3 15/16 in)
Centre-to-centre spacing: 5.42 in (5 7/16 in)
Equal spaces across the run: 18 spaces
Largest gap allowed: 4 in
Item 1, centre from the start: 4.67 in (4 11/16 in)
Item 2, centre from the start: 10.08 in (10 1/16 in)
Item 3, centre from the start: 15.5 in (1 ft 3 1/2 in)
Item 4, centre from the start: 20.92 in (1 ft 8 15/16 in)
Item 5, centre from the start: 26.33 in (2 ft 2 5/16 in)
Item 6, centre from the start: 31.75 in (2 ft 7 3/4 in)
Item 7, centre from the start: 37.17 in (3 ft 1 3/16 in)
Item 8, centre from the start: 42.58 in (3 ft 6 9/16 in)
Item 9, centre from the start: 48 in (4 ft 0 in)
Item 10, centre from the start: 53.42 in (4 ft 5 7/16 in)
Item 11, centre from the start: 58.83 in (4 ft 10 13/16 in)
Item 12, centre from the start: 64.25 in (5 ft 4 1/4 in)
Item 13, centre from the start: 69.67 in (5 ft 9 11/16 in)
Item 14, centre from the start: 75.08 in (6 ft 3 1/16 in)
Item 15, centre from the start: 80.5 in (6 ft 8 1/2 in)
Item 16, centre from the start: 85.92 in (7 ft 1 15/16 in)
Item 17, centre from the start: 91.33 in (7 ft 7 5/16 in)

Final result17 items

Confidence note: Every space is the same, the first and last included, and every mark is measured from the start of the run, rounded on its own to the nearest 1/16 in (1.6 mm) in imperial and given exactly in millimetres in metric.

What this calculation does not cover

The count holds every space at or under the maximum entered, and that maximum is the reader's to find: a guard's opening limit from the building code that applies, which is the IRC's 4 in (101.6 mm) sphere in the United States and 100 mm (3.94 in) under England's Approved Document K and Canada's National Building Code; a fixing pitch from the product's instructions; a span from a table. The page compares a spacing with the figure given; it does not decide which figure the work is held to.
Every item is taken to be the width entered and to stand square to the run. A spindle that is turned or tapered, a post wider at its base than higher up, or a batten fixed at an angle needs its width measured at the height where the gap is measured, or the gaps come out tighter or wider than shown.
With gaps at both ends the run is the clear distance between the end posts or walls, and the first and last spaces equal the rest. Starting from a centred item, or leaving a different gap at one end, changes every figure here. With a centres limit and gaps at both ends, the end faces are treated as supports as wide as the items.
The marks are distances from the start of the run, each rounded to the nearest 1/16 in (1.6 mm) on its own. Stepping a spacer block from item to item, or hooking the tape on the last item fixed, carries every small error into the next space and gathers them all into the last one.
Spacing is the only thing worked out. The opening under a bottom rail, a guard's height, a post's footing, the strength of the items and a fixing's distance from an edge are separate questions with their own rules. For studs or joists that board edges must land on, the standard centres are kept and the last bay is short, which is a different layout from this one.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-10-05 · v1.0.0

Regulatory standards & verification citations3

International Residential Code R312.1.3 — openings in a required guard must not allow passage of a 4 in (101.6 mm) diameter sphere; one example of the maximum a reader enters
Approved Document K (2013 edition), Section 3 — guarding in a building likely to be used by children under five should not have openings that allow passage of a 100 mm (3.94 in) sphere; the metric example
NIST Handbook 44 (2026 edition), Appendix C: 12 inches = 1 foot and 1 inch = 2.54 centimetres exactly, the basis of the tape readings and of the millimetres a metric reader is shown

Which documents these citations point at

International Residential Code — R312.1.3 (United States)One- and two-family dwellings and townhouses up to three storeys — structure, fire safety, energy, plumbing, mechanical and electrical in a single document.
Approved Documents to the Building Regulations (England) — K (United Kingdom)Practical guidance on meeting the Building Regulations, one lettered part per subject — Part A structure, Part B fire, Part K protection from falling, Part L conservation of fuel and power, and the rest.

A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

How to calculate equal spacing (balusters or spindles, posts, battens) in 9 steps

Length of the RunThe distance the items are spread across, measured between the faces they start and finish against.
Width of Each ItemThe face width of one baluster, post, batten or fixing, measured along the run; 0 for marks to points.
How the Run Starts and FinishesA gap at each end, for balusters between two posts; or an item at each end, for a line of posts or battens.
CountLet the page find the count from a maximum spacing, or give the count and get the spacing.
The Maximum Applies ToA guard's opening limit is a clear gap; a fixing pitch or a span is usually given as centres.
Largest Spacing AllowedThe most the gap or centres may be, from your code, the maker's instructions or the design: 100 mm (3.94 in) and 4 in (101.6 mm) are guard-opening limits.
Number of ItemsHow many items to space out, counting the end items if the run starts and finishes on one.
Marks ToWhere each mark is measured to: the middle of the item, or the edge nearer the start of the run.
Items to set outThe tool computes the items to set out from those figures and shows the formula, its sources, and a confidence rating alongside it.

Items to set out by length of the run

Page defaults, not your figures above.

Length of the Run	Items to set out (items)
4 ft	8
6 ft	13
8 ft	17
10 ft	21
12 ft	26
14 ft	30

Frequently asked questions

How do I space balusters evenly between two posts?: Choose a gap at each end, enter the clear distance between the posts, the baluster's face width and the largest gap your code allows, and keep the maximum on the clear gap. The page gives the fewest balusters that keep every gap at or under it, the gap they actually leave, and where each one goes measured from the first post. On an 8 ft (2.44 m) bay of 1.5 in (38 mm) balusters held to 4 in (101.6 mm), that is 17 balusters with gaps of 3.92 in (99.5 mm), marked at 3 15/16 in.
What is the difference between the gap and the centres?: The gap is the clear space between two neighbouring items, face to face; the centres are measured from the middle of one item to the middle of the next. The centres are always one item's width more than the gap. Guard openings are limited as a clear gap; fixings, posts and joists are usually specified at centres.
Should the run start and finish on a post or on a gap?: On a gap when the ends are already fixed, as with balusters between newel posts or battens between two walls: the end posts are not counted and the end spaces equal the others. On an item when the first and last of the things being spaced sit at the ends, as with a line of fence posts or a row of fixings along a rail: those two are counted, and the run is measured over their outside faces.
Why are the marks measured from one end instead of from item to item?: Because every measurement carries a small error, and stepping from one item to the next adds each error to the one before. Measured from a single starting point, each mark carries only its own rounding, so the last space comes out the same as the first. Hook the tape once at the start and mark every figure from it.
Can I use this for stud or joist layout?: Only where nothing has to land on the members. Studs and joists under sheet materials are set at a fixed centre, 16 in or 24 in (406 mm or 610 mm) in North America and 400 mm or 600 mm (15.7 in or 23.6 in) in the UK, so that board edges fall on them, and the last bay is simply short. Equal spacing would move every member off the board joints. The stud calculator lays framing out that way.
How is this different from the deck baluster calculator?: The baluster calculator counts the balusters in one bay against the guard's sphere for your unit system, and gives the gap they leave. This page takes any item and any maximum, gap or centres, starts and finishes the run either way, accepts a count you choose instead, and lists the mark for every item.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.