Stair Calculator
Calculate risers, treads, stringer length and total run from your total rise.
What you need
14
Number of risers — Steps up. There is always one fewer tread than riser on a standard flight.
- Actual riser height
- 7.50 in
- Number of treads
- 13
- Total horizontal run
- 11.4 ft
- Stringer length (minimum board)
- 14.4 ft
- Total stringer material
- 43.1 ft
- Tread material needed
- 41.0 ft
- Stair angle (degrees)
- 37.6
Total rise divided evenly. All risers must be within 3/8 in of each other.
Floor space the stair occupies. Check it fits before you cut anything.
Diagonal length. Buy longer — you cannot stretch a stringer.
30 to 35° is comfortable. Over 37° feels steep and is often out of code.
Estimates for planning. Confirm quantities with your supplier before ordering — see the assumptions below for the figures used.
How to use the stair calculator
Stairs are the one part of a build where being slightly off is genuinely dangerous, and code is specific about it. Enter your total rise — finished floor to finished floor — and this works out the riser count, exact riser height, tread depth and stringer length, and flags anything outside typical code limits.
What this calculator assumes
Every estimate depends on figures that vary by supplier and conditions. These are the ones used here, so you can sanity-check the result against your own quote.
- Riser count is chosen to land as close as possible to your preferred riser height, then the total rise is divided evenly between them. Every riser in a flight must be within 3/8 in of every other — uneven risers are a trip hazard and a code violation.
- A standard straight flight has one fewer tread than risers, because the top riser lands on the finished floor above.
- Typical residential code limits are a 7¾ in maximum riser and a 10 in minimum tread, with 36 in minimum width and 6 ft 8 in minimum headroom. Your jurisdiction governs, and these numbers do vary.
- Stringer length is the straight diagonal. Buy stock longer than the figure shown — cutting the notches consumes length and there is no recovering from a short stringer.
- Handrails, guards, nosing projection, landings and headroom are not calculated here and are all code-regulated. Stairs almost always require a permit and inspection.
Frequently asked questions
What is the ideal stair riser height?
Seven to seven and a half inches is the comfortable range, with residential code commonly capping risers at 7¾ inches. Consistency matters more than the exact figure: your foot learns the rhythm after two steps, and a single riser that differs by half an inch is where people fall.
How do I calculate the number of stairs?
Divide the total rise by your target riser height and round to the nearest whole number — that is your riser count. Then divide the total rise by that count to get the exact riser height. A 105 inch rise with a 7¼ inch target gives 14 risers at exactly 7.5 inches each.
What is the 7-11 rule for stairs?
A 7 inch riser with an 11 inch tread, widely considered the most comfortable combination for a straight residential flight. Related rules of thumb are that riser plus tread should total 17 to 18 inches, and that two risers plus one tread should come to 24 to 25 inches.
How long a board do I need for a stair stringer?
Take the square root of the rise squared plus the run squared, then buy longer. A 105 inch rise with a 136 inch run gives a 172 inch diagonal — about 14⅓ feet — so you would buy 16 foot stock. Notching eats into the board, and 2x12 is the usual minimum size for a cut stringer.
How much space do stairs take up?
More than most people expect. A typical flight climbing 9 feet needs about 11 to 12 feet of horizontal run plus a landing at each end. Check the total run against your floor plan before committing — this is the most common reason a stair has to be redesigned.
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