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Stair Calculator

Enter the total rise (floor to floor) and get a code-compliant stair layout: number of steps, the exact riser and tread for each, total run, and the 2×12 board length your stringers need.

Diagram of a staircase showing total rise and total run split into equal steps
Total rise is floor to floor; the calculator splits it into equal, legal steps.

Your buy-list

Enter your measurements

How the stair layout is calculated

The design starts from the International Residential Code (IRC R311.7.5): riser height may not exceed 7-3/4 in, tread depth may not be less than 10 in, and every riser in a flight must be equal (the code allows no more than 3/8 in variation. Equal risers make the stairs safe to walk half-asleep).

So: risers = total rise ÷ 7.75, rounded up, the fewest steps that keep each riser legal. The actual riser is then total rise ÷ risers, an equal share. Tread depth follows the classic comfort rule 2 × riser + tread = 25 in, floored at the 10 in code minimum. A 7.38 in riser pairs with a 10.23 in tread: 2 × 7.38 + 10.23 = 25, right on the rule (the famous 7/11 step, a 7 in riser with an 11 in tread, is the same idea from the other direction).

Treads = risers − 1. The upper floor is the last step, so there's one fewer tread than risers. Total run = treads × tread depth. The stringer length is the hypotenuse, √(rise² + run²); stringers are cut from 2×12 stock, and the buy-list rounds up to the next standard board length.

Sources

The figures behind this calculator come from published manufacturer data and industry standards:

Worked examples

8 ft floor-to-floor (typical storey)

96 in rise ÷ 7.75 → 13 risers of 7.38 in; treads 10.23 in; run 10.23 ft.

13 risers, 12 treads: 14 ft stringer boards

6 ft deck rise

72 in rise → 10 risers of 7.2 in; treads 10.6 in; run 7.95 ft.

10 risers, 9 treads: 10 ft stringer boards

9 ft floor-to-floor (tall ceilings)

108 in rise → 14 risers of 7.71 in; treads at the 10 in minimum; run 10.83 ft.

14 risers, 13 treads: 16 ft stringer boards

Frequently asked questions

What is the maximum riser height allowed by code?
7-3/4 in under the IRC for homes. The IRC sets no minimum riser height. The 4 in minimum (with a 7 in maximum) comes from the IBC, which covers commercial work. The largest riser in a flight can exceed the smallest by at most 3/8 in, which is why this calculator divides the total rise into perfectly equal risers.
How many steps do I need for an 8 ft ceiling?
Measure floor to floor: usually about 9 ft once the joists and subfloor are in, even for an '8 ft ceiling' room. At exactly 96 in of rise it's 13 risers / 12 treads; at 108 in it's 14 / 13. Always design from the measured total rise, never the ceiling height.
Why is there one less tread than risers?
The top riser takes you onto the upper floor itself. That floor is the final 'tread', and you don't build a step for it. Every stair works this way: N risers, N−1 treads.
How long a 2×12 do I need for the stringer?
The stringer is the diagonal: √(total rise² + total run²). An 8 ft rise layout needs 12.99 ft of diagonal, so 14 ft boards. Buy one extra board if you've never cut stringers. The first one is a template and a mistake allowance in one.
What about headroom and landings?
The IRC also requires 6 ft 8 in of headroom over the stair and a landing at top and bottom. Those depend on your floor opening and layout, not just the rise. Check them against your local code before you cut.

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Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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