Balustrade & railing tool
Spindle Spacing Calculator
How many stair spindles you need, the gap between them, and the pitch line they hang from — checked against the 100mm and 4in sphere rules. Free, no account needed.
Finished floor to finished floor.
7-7.5in is comfortable; risers are equalised.
Horizontal depth, nosing excluded.
Plumb from the nosing line to the ceiling above.
Landings, stringers & handrail
Half-landings or quarter-turns in this flight.
16in suits most treads; 12in for thin or composite.
Measured above the nosing line.
4in (100mm) sphere rule.
Sets the bottom stringer drop.
Your flight
15 risers × 7.33in
14 treads at 10.50in / 26.7cm · 36.8 degree pitch
- Riser height (equal)
- 7.33in / 18.6cm
- Tread run (going)
- 10.50in / 26.7cm
- Total run
- 147.00in / 373.4cm
- Cut line (diagonal)
- 183.60in / 466.3cm
- Stringer stock length
- 195.60in / 496.8cm (16.3ft)
- Pitch
- 36.8 degrees
- 2R + G
- 25.17in / 63.9cm
- Stringers
- 4 at 12.0in centres (65.2ft stock)
- Handrail length
- 207.60in / 527.3cm (17.3ft)
- Balusters
- 39 at 5.2in centres
Code & comfort checks
IRC (US) allows a maximum 7.75in riser. Every riser in a flight must match within 3/8in.
Minimum going is 10.00in. Shallow treads are the single biggest cause of descending falls.
Comfortable domestic flights sit between 30 and 37 degrees; 42 degrees is the absolute ceiling.
Two risers plus one going should land between 24in and 25in (600-640mm) for a natural stride.
IRC (US) expects at least 36.0in of clear width above the handrail height.
Minimum headroom is 80in measured plumb from the tread nosing line.
IRC wants a graspable handrail 34-38in above the nosing line, continuous for the full flight, and no gap that passes a 4in sphere.
Guidance only — confirm against your local building control before you cut or pour.
Compare riser counts
| Risers | Riser | Going | Run | Pitch |
|---|---|---|---|---|
| 14 | 7.86in | 10.50in | 11.4ft | 38.9° |
| 15 | 7.33in | 10.50in | 12.3ft | 36.8° |
| 16 | 6.88in | 10.50in | 13.1ft | 34.9° |
The highlighted row is your current flight. Nudging the riser count is usually the cheapest way to bring a steep or shallow stair back inside code.
Advanced layout
Mark-out schedule, framing deductions & take-off
Step-by-step mark-out
| Step | Height above floor | Run from first riser |
|---|---|---|
| 1 | 7.33in / 18.6cm | 10.50in / 26.7cm |
| 2 | 14.67in / 37.3cm | 21.00in / 53.3cm |
| 3 | 22.00in / 55.9cm | 31.50in / 80.0cm |
| 4 | 29.33in / 74.5cm | 42.00in / 106.7cm |
| 5 | 36.67in / 93.1cm | 52.50in / 133.3cm |
| 6 | 44.00in / 111.8cm | 63.00in / 160.0cm |
| 7 | 51.33in / 130.4cm | 73.50in / 186.7cm |
| 8 | 58.67in / 149.0cm | 84.00in / 213.4cm |
| 9 | 66.00in / 167.6cm | 94.50in / 240.0cm |
| 10 | 73.33in / 186.3cm | 105.00in / 266.7cm |
| 11 | 80.67in / 204.9cm | 115.50in / 293.4cm |
| 12 | 88.00in / 223.5cm | 126.00in / 320.0cm |
| 13 | 95.33in / 242.1cm | 136.50in / 346.7cm |
| 14 | 102.67in / 260.8cm | 147.00in / 373.4cm |
Deduct one tread thickness so the first riser matches the rest.
Taken off the top of the stringer when the top tread is the finished floor.
Horizontal distance before the ceiling opening clears the nosing line.
Trimmer-to-trimmer opening in the floor above to keep headroom legal.
Includes 12in of extra length per board for the top and bottom cuts.
Board, stone or laminate for the tread faces including nosings.
Paint, stain, carpet or stone coverage for the whole flight.
Includes a 10% waste margin; refine it in the runner calculator.
Like these numbers? Save this flight, attach it to a client project and quote it with a free Riser account.
Continue in Riser — freeQuick answer
How do you calculate spindle spacing on a staircase?
To calculate spindle spacing, measure the clear run between the newel posts, then divide it by the maximum gap plus one spindle width. The gap must never let a 4in (100mm) sphere pass, so with a 1 1/4in square spindle the centres land at about 5 1/4in and most stairs end up with two spindles per tread. Round the spindle count up to a whole number and recalculate the gap so it falls comfortably under the limit, and set the spacing along the pitch line rather than the floor.
- Spindles = ceil(clear run / (max gap + spindle width)); recalculate the gap after rounding.
- No gap may pass a 4in / 100mm sphere, including the triangle at the foot of a raking rail.
- Two spindles per tread is the normal answer on a 10in going or a 220mm+ UK going.
- Spacing is set horizontally along the pitch line; every spindle on a rake is a different length.
- UK rail heights: 900mm on the flight, 1100mm on landings. US: 34-38in on the flight.
- Always measure the clear run after the newels are fixed, never from the drawing.
Start with the clear run, not the drawing
Spindle spacing is arithmetic done on one measurement: the clear run of handrail between the two newel posts. Take it after the newels are permanently fixed, face to face, at the height the spindles will actually sit. Drawings are almost always a few millimetres out once the posts are trimmed and wedged, and a few millimetres spread over ten gaps is enough to push the end gap past the limit.
| Clear run | Spindle width | Spindles needed | Resulting gap | Verdict |
|---|---|---|---|---|
| 1000mm | 32mm | 8 | 84.4mm | Passes |
| 1200mm | 32mm | 10 | 80.0mm | Passes |
| 1500mm | 32mm | 13 | 82.9mm | Passes |
| 1800mm | 41mm | 15 | 83.7mm | Passes |
| 2100mm | 41mm | 18 | 83.9mm | Passes |
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Open the stair runner calculatorThe sphere test in plain terms
Every opening in a stair guard is tested with a sphere: 100mm in the UK under Approved Document K, 4in in the US under the IRC. The sphere is pushed into the widest part of the gap, not the average, and that includes the triangular opening formed where a raking handrail crosses a tread and riser. A balustrade that measures perfectly between spindles can still fail at that triangle, so check it separately once the rail is set.
- Test the gap next to each newel — it is usually the widest.
- Test the triangle at the foot of a raking rail with the gauge pushed hard into the corner.
- Landings need the same test at 1100mm rail height in the UK.
- Horizontal infill and cable runs are also tested for deflection, not just static gap.
Marking out a raking flight
On a level landing the spindles are identical. On a flight they are not. Set the horizontal spacing along the pitch line — the line joining the tread nosings — then plumb each mark up to the underside of the handrail and cut. Lengths increase in a fixed step: riser height divided by spindles per tread. Cut in sequence, label each one as it comes off the saw, and dry-fit the whole run before glue touches a mortice.
Geometry first, balustrade second
A spindle schedule built on an approximate rise and going has to be redone. Settle the riser height, going and pitch here first, then fix the newels, then divide the clear run for spindles.
Ordering: spindles, newels and the bits people forget
Once the count is settled the order is predictable, and the parts people forget are the ones that hold a job up: base rail and handrail in matching profile, fillet strips or spacers, newel caps and bases, and fixings rated for the rail. Order 5-10% extra spindle stock on a turned or figured timber, because a split at the mortice on a long spindle is a wasted piece rather than a repair.
If a fitted runner is going down the same flight, the balustrade and the runner interact: the spindles eat into the visible tread width, and the runner has to leave an even margin of timber on each side. Work the width out with the stair runner width calculator, and get the length from the stair runner calculator on the home page once the going, riser and nosing are locked in — the same three numbers drive both jobs.
Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.
Still deciding on material, width or pattern? Our hub on stair runners compares weaves, widths, backings and fitting styles side by side, then hands the numbers straight to the calculator.
Frequently asked questions
What is the maximum gap between stair spindles?
Under 100mm in the UK and under 4in in the US, tested with a sphere at the widest point of every opening. Because 100mm is 3.94in, a UK-compliant design always satisfies the American figure. Building control checks the worst gap they can find, which is usually the one next to a newel or the triangle under a raking handrail, so design to the tightest opening rather than the average.
How many spindles do I need per step?
Two on almost every domestic staircase. A 10in or 250mm going with 1 1/4in spindles gives three gaps of roughly 3 1/4in, comfortably inside the limit. Deep treads, bullnose steps and landings often take three, and a tight winder can occasionally work with one plus the newel, provided every resulting gap still passes the sphere test.
How do I space spindles evenly between newel posts?
Measure the clear run face to face between the newels, decide the spindle width, then divide the run by the maximum gap plus one width and round up. Divide the leftover run equally so the first and last gaps match the middle ones — an unequal end gap is the single most common reason a balustrade looks wrong even when it passes inspection.
Does spindle spacing change on a sloping flight?
The horizontal spacing stays constant; the lengths do not. Each spindle climbs the rake, so its length grows by the riser height divided by the number of spindles per tread. With a 190mm riser and two per tread, that is 95mm added to each successive spindle. Mark spacing along the pitch line and transfer it up to the underside of the handrail with a plumb bob or laser.
Do fillets or base rails change the calculation?
Yes, and helpfully so. A base rail with fillet strips fixes the gap mechanically: you cut fillets to the gap you calculated and the spindles cannot drift. Order fillet stock by the total run rather than per gap, and confirm the fillet length matches the calculated gap exactly before you cut the whole run.
What size spindles should I buy?
32mm (1 1/4in) and 41mm (1 5/8in) square stock cover most domestic staircases, with 90mm and 100mm newels. Wider spindles reduce the gap for the same centres, so a 41mm spindle lets you space slightly further apart for the same compliance. Turned spindles are measured at the square block, not the narrowest turning.
Is this spindle spacing calculator free?
Yes. The geometry, pitch, rise and run, pitch line and code checks are all free with no account. A free Riser account only matters if you want the flight saved to a project so the same spacing schedule can be reused, quoted or sent to a client.
Related tools & guides
Start with the numbers: our stair runner calculator also works as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length first time.