Stair Calculator

Risers, treads, total run and stringer length from your floor-to-floor height, checked against the residential building code.

Risers (steps up) 15 risers 15 risers of 7.20 in and 14 treads, 12.25 ft of total run.

Steps

Actual riser height: 7.20 in
Treads: 14 treads
Total run: 147 in
Total run: 12.25 ft

Stringers

Stringer length (approx.): 15.20 ft
Buy stringer boards at least: 16 ft long
Stair angle: 36.3 degrees

How many stairs do I need?

Divide the total rise (floor to floor, in inches) by your target riser height and round up: that's the number of risers. Divide the total rise by that number for the exact riser height. You need one tread fewer than risers. For 108 in floor to floor and a 7.5 in target, that's 15 risers of 7.20 in and 14 treads. The residential code allows risers up to 7¾ in and treads of at least 10 in.

Worked example: 108 inches floor to floor

Risers: 108 ÷ 7.5 = 14.4, round up to 15 risers.
Exact riser height: 108 ÷ 15 = 7.20 in, under the 7¾ in maximum.
Treads: 15 − 1 = 14 treads (the top step is the upper floor).
Total run: 14 × 10.5 in = 147 in = 12.25 ft of floor space.
Stringers: √(108² + 147²) ≈ 182 in = 15.20 ft, so buy 16 ft boards. The stairs climb at about 36.3°.

Steps for common floor-to-floor heights

With a 7.5 in target riser and 10.5 in treads.

Total rise	Risers	Riser height	Total run
24 in (deck)	4	6.00 in	31.5 in
36 in (deck)	5	7.20 in	42 in
96 in (8 ft)	13	7.38 in	126 in
108 in (9 ft)	15	7.20 in	147 in
120 in (10 ft)	16	7.50 in	157.5 in

Residential code limits (IRC)

Riser height: no more than 7¾ in (R311.7.5.1).
Tread depth: at least 10 in (R311.7.5.2).
Consistency: within a flight, the tallest riser and the deepest tread may not exceed the smallest by more than ⅜ in.
Headroom: at least 6 ft 8 in above the stairs (R311.7.2).
Handrail: required on stairs with 4 or more risers (R311.7.8).

Your local code may differ, so check with your building department before you cut stringers.

Measuring the total rise

Measure from the finished floor at the bottom to the finished floor at the top. If flooring isn't installed yet, add its thickness, or the first or last step will end up a different height from the rest. On sloping ground, measure where the bottom step will actually land.

Frequently asked questions

What is the maximum stair riser height?

7¾ inches under the International Residential Code (R311.7.5.1). 7 to 7½ in is more comfortable.

What is the minimum tread depth for stairs?

10 inches under the International Residential Code (R311.7.5.2), measured without the nosing.

How many steps for an 8 ft ceiling?

For 96 inches floor to floor with a 7.5 in target: 13 risers of about 7.38 in and 12 treads. Measure your actual floor-to-floor height, which includes the floor structure.

How long should stair stringers be?

Roughly √(total rise² + total run²). For 108 in of rise and 147 in of run, about 182 in (15.2 ft), so buy 16 ft boards.

Why is there one less tread than risers?

The last step up lands on the upper floor, which acts as the top tread.

Guides

Stair Rise and Run: Code Rules and How to Calculate

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Sources and method

Kitsap County (WA) — residential final inspection checklist, quoting IRC R311.7 — risers max 7¾ in, treads min 10 in, ⅜ in variation, 6 ft 8 in headroom, handrails at 4+ risers

Last checked October 12, 2026. How we build and test every calculator: methodology.