Stair Calculator: Rise, Run, Steps & Stringer Length

Enter the total rise, the maximum riser height you want and the tread depth. The calculator works out the number of steps, the exact riser height, the total run and the stringer length, and checks them against common code limits.

Total rise (floor to floor, or deck to ground)

Maximum riser height

Tread depth (run per step)

Stair width

Stringer spacing

–steps (risers)

–riser height

–treads

–total run

–stringer length

Checks use common US building code limits. Your local code may differ, so confirm before you build.

How to measure the total rise

Inside stairs: measure from the finished floor at the bottom to the finished floor at the top. Include flooring that isn’t laid yet.
Deck stairs: measure from the top of the deck boards straight down to where the bottom step will land. Ground often slopes, so measure at the actual landing spot, not at the deck edge.

How the calculator works

Number of risers = total rise ÷ maximum riser height, rounded up
Riser height = total rise ÷ number of risers, so every step is the same
Number of treads = risers − 1, because the top step is the floor or deck itself
Total run = treads × tread depth
Stringer length = √(total rise² + total run²)

Worked examples

Inside stairs, 8 ft 4 in floor to floor (100 in): 100 ÷ 7.5 = 13.3, so 14 risers of 7⅛ in. With 13 treads of 10½ in, the total run is 11 ft 4½ in. The stringer is about 14 ft 1¼ in long, so buy 16 ft boards.

Deck steps, 36 in high: with a 7¾ in maximum, that’s 5 risers of 7 3/16 in and 4 treads. At 10½ in treads the run is 3 ft 6 in, and an 8 ft board is long enough for each stringer.

Common code limits for home stairs

Rule	Common US limit
Maximum riser height	7¾ in
Minimum tread depth	10 in
Largest difference between risers	⅜ in
Minimum headroom	6 ft 8 in
Minimum stair width	36 in
Handrail	Required with 4 or more risers

These are based on the International Residential Code, which most US areas use. Local codes can differ, so confirm with your building department.

Comfortable stairs

Stairs feel natural when 2 risers + 1 tread adds up to about 24 to 25 inches. A 7 in riser with a 10½ to 11 in tread is a classic, easy stride. Very steep or very shallow stairs both feel awkward and cause trips.

Cutting stringers

Most stringers are cut from 2×12 lumber, which leaves enough wood below the notches.
Use a framing square with stair gauges set at your riser height and tread depth to mark each step.
Trim the bottom of the stringer by the thickness of one tread, so the first step ends up the same height as the rest.
Space stringers about 16 inches apart for most treads. Composite treads may need closer spacing, so check the maker’s instructions.