Stair Layout Calculator
Divide the total rise by your maximum riser height and round up — that is the riser count; total rise ÷ count gives the exact riser height. A 105 in floor-to-floor rise at a 7¾ in maximum works out to 14 risers of exactly 7½ in, 13 treads, and 130 in of total run with 10 in treads.
- Risers
- 14
- Exact riser height
- 7.5 in7 1/2"
- Treads
- 13
- Total run
- 130 in10' 10"
- 2R + T comfort
- 25 ininside the 24–25 in band
Defaults follow IRC R311.7.5: 7¾ in max riser, 10 in tread. Verify against local code.
Enter the total rise (finished floor to finished floor) and the calculator returns the riser count, the exact riser height to cut, the tread count, the total run the staircase needs, and the 2R + T comfort number. Imperial defaults follow IRC R311.7.5 (7¾ in max riser, 10 in tread); metric defaults follow DIN 18065 practice (190 mm riser, 250 mm tread).
Measure the rise after flooring decisions are made — tile downstairs and hardwood upstairs shift the first and last riser. Codes also cap riser variation (IRC: ⅜ in between the tallest and shortest), which is why the whole point is dividing the rise into equal risers.
Formula
risers = ⌈rise ÷ max riser⌉ · riser height = rise ÷ risers · treads = risers − 1 · run = treads × tread depth
- Measure the total rise: finished floor to finished floor, including flooring build-up on both levels.
- Pick the maximum riser your code allows: 7¾ in under IRC R311.7.5 (US residential); DIN 18065 keeps residential risers around 14–20 cm.
- Risers = total rise ÷ max riser, rounded up — always up, or the risers come out over the limit.
- Exact riser height = total rise ÷ riser count. Every riser is cut to this one number.
- Treads = risers − 1, because the upper floor is the final step. Total run = treads × tread depth.
- Comfort check: 2 × riser + tread should land near 24–25 in, or 630 ± 30 mm by DIN 18065's step rule (Schrittmaßregel).
Worked example: 105 in floor-to-floor
Given
- Total rise 105 in
- Max riser 7¾ in (IRC R311.7.5)
- Tread depth 10 in
Steps
- Risers: 105 ÷ 7.75 = 13.55 → round up to 14
- Exact riser height: 105 ÷ 14 = 7.50 in
- Treads: 14 − 1 = 13
- Total run: 13 × 10 = 130 in (10' 10")
- Comfort: 2 × 7.5 + 10 = 25 — inside the 24–25 in band
Lay out 14 risers at exactly 7½ in and 13 treads at 10 in — 130 in of run. Keep riser-to-riser variation within ⅜ in, and re-check the first and last riser after the flooring goes down.
Frequently asked questions
What is the maximum stair riser height by code?
Under the US IRC (R311.7.5, residential): riser max 7¾ in, tread min 10 in, and no more than ⅜ in variation between the largest and smallest riser. German DIN 18065 keeps residential risers around 14–20 cm. Local amendments override both — verify the code that applies to your project.
What is the 2R + T comfort rule?
Twice the riser plus the tread should match a natural stride: about 24–25 in, or 630 ± 30 mm in DIN 18065's step rule. The worked example lands exactly on 25 (2 × 7.5 + 10). Stairs far outside the band feel too steep or force a shuffle.
Why is there one fewer tread than risers?
The upper finished floor acts as the last tread. Fourteen risers lift you through fourteen height changes, but you only step on thirteen treads before standing on the floor above.
Why do all risers have to be equal?
An odd riser is a trip hazard — feet learn the rhythm within two steps. That is why codes cap total variation (IRC: ⅜ in) and why you divide the rise evenly instead of stacking code-max risers plus one short one.
How much total run does a staircase need?
Treads × tread depth, plus any landings. The 105 in example needs 130 in (about 3.3 m) of horizontal run. If the run doesn't fit, code permitting you can steepen toward the max riser, deepen the plan with a landing and turn, or relocate the stair.
Stair code differs by jurisdiction and stair type — headroom, guards, nosing, width, and egress rules all apply on top of riser and tread limits. Estimate only — verify against local code before you cut stringers.
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