Carpentry tool
Stair Tread Calculator
How many treads you need, the going, the nosing overhang and the board depth to buy — with total run, pitch and code checks from a single set of measurements.
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
Quick answer
How do you calculate stair treads?
The number of treads is the riser count minus one when the top step is the finished upper floor, or equal to the riser count when there is a full tread at the top. Tread run is the horizontal depth from the face of one riser to the face of the next, excluding the nosing overhang; total tread depth is the run plus the nosing, which is usually 3/4in to 1 1/4in. Divide the available horizontal run by the tread count to size treads for a fixed opening, and keep the run at 10in or more.
- Treads = risers minus one when the top step is the upper floor.
- Tread run is measured riser face to riser face, nosing excluded.
- Total tread depth = run + nosing overhang (3/4in to 1 1/4in typical).
- Fixed opening: tread run = available run divided by the tread count.
- Minimum run is 10in (IRC) or 220mm going (UK); 10.5in is comfortable.
- Every tread in a flight must match within 3/8in.
Treads follow risers
You cannot size treads until the risers are settled, because the tread count comes out of the riser count. Divide total rise by a target riser, round to a whole number, then decide what happens at the top: if the upper floor is the top step you have one fewer tread than risers, and if a full tread sits at the top the counts match.
| Risers | Treads (flush top) | Going | Nosing | Board depth | Total run |
|---|---|---|---|---|---|
| 13 | 12 | 10.00in | 1.00in | 11.00in | 120in |
| 14 | 13 | 10.50in | 1.00in | 11.50in | 136.5in |
| 15 | 14 | 10.50in | 1.25in | 11.75in | 147in |
| 16 | 15 | 11.00in | 1.00in | 12.00in | 165in |
| 18 | 17 | 11.00in | 1.25in | 12.25in | 187in |
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 calculatorNosing: small number, big consequences
The nosing is the lip that projects past the riser below. Codes want 3/4in to 1 1/4in on closed-riser stairs, and it must be consistent within 3/8in from step to step. It changes the board you buy, the perceived tread depth underfoot and — if the flight is going to be carpeted — the runner length, because the runner has to wrap the nose of every tread.
- Going is what code measures; nosing is added on top for the board size.
- Keep the nosing identical on every step, including the bottom one.
- Open-riser and most deck stairs run zero nosing.
- A deeper nosing does not buy you a deeper going — the code minimum still applies to the going.
Treads and the finished surface
Whatever goes on top of the tread — carpet, a runner, stone or a stained hardwood face — is sized from the same numbers. The advanced panel adds a surface-area take-off for the whole flight and an approximate runner length, and the stair runner calculator on the home page turns the going, riser and nosing into an exact runner order with landings and pattern repeat allowed for.
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.
Frequently asked questions
How many treads do I need for my stairs?
Count the risers first: total rise divided by a 7-7.5in target riser, rounded to a whole number. Treads are one fewer than risers when the top step is the finished floor above, and equal to the risers when a full tread sits at the top. A 110in rise gives 15 risers and 14 treads.
What is the difference between tread run, tread depth and going?
Tread run — the UK calls it the going — is the horizontal distance from one riser face to the next, and it is the figure codes measure. Tread depth usually means the physical board including the nosing overhang, so a 10.5in going with a 1in nosing needs an 11.5in board.
What is the minimum stair tread depth?
The IRC requires a 10in minimum run with a nosing of 3/4in to 1 1/4in where the riser is closed. UK Approved Document K sets a 220mm minimum going on private stairs. Anything shallower puts the ball of the foot over the edge on the way down, which is when falls happen.
How wide should stair tread boards be?
Add the going and the nosing, then round up to available stock: an 11.5in requirement usually means a 1x12 or a purpose-made 11 1/4in stair tread. Buy treads slightly over-length and cut to the finished stair width once the stringers are fixed, since few openings are perfectly parallel.
How do I fit treads into a fixed opening?
Tick 'fit the flight into a fixed opening' and enter the horizontal space. The calculator divides that run into equal treads for the riser count and warns you when the resulting going drops under the code minimum — the point at which you genuinely need a landing or winders instead of shallower treads.
Do I need an account for the tread schedule?
No account for the tread count, run, total run, nosing and code checks. A free account unlocks the step-by-step mark-out schedule, framing deductions and surface-area take-off, and the same tool sits in the Riser portal where flights save to a project and become quotes.