Stair Calculator
Enter your total rise to get the number of steps, exact riser height, total run, stringer length and how many stringers to cut, with every result checked against the residential stair code.
Risers = total rise ÷ 7.75 in, rounded up. Riser height = total rise ÷ risers. Treads = risers − 1. A 9 ft (108 in) rise needs 14 risers of 7 11/16 in and 13 treads; with 10 ½ in treads the stairs run 11.4 ft and each stringer is about 15.6 ft long.
Stair dimensions for common heights
Using the 7.75 in maximum riser and 10.5 in treads. Treads are one fewer than risers because the top step is the floor or deck.
| Total rise | Risers | Riser height | Treads | Total run | Stringer length |
|---|---|---|---|---|---|
| 24 in (2 ft) | 4 | 6 in | 3 | 2.6 ft | 4.3 ft |
| 30 in (2.5 ft) | 4 | 7 1/2 in | 3 | 2.6 ft | 4.7 ft |
| 36 in (3 ft) | 5 | 7 3/16 in | 4 | 3.5 ft | 5.7 ft |
| 48 in (4 ft) | 7 | 6 7/8 in | 6 | 5.3 ft | 7.6 ft |
| 60 in (5 ft) | 8 | 7 1/2 in | 7 | 6.1 ft | 9.0 ft |
| 72 in (6 ft) | 10 | 7 3/16 in | 9 | 7.9 ft | 11.0 ft |
| 84 in (7 ft) | 11 | 7 5/8 in | 10 | 8.8 ft | 12.3 ft |
| 96 in (8 ft) | 13 | 7 3/8 in | 12 | 10.5 ft | 14.3 ft |
| 108 in (9 ft) | 14 | 7 11/16 in | 13 | 11.4 ft | 15.6 ft |
| 120 in (10 ft) | 16 | 7 1/2 in | 15 | 13.1 ft | 17.6 ft |
| 132 in (11 ft) | 18 | 7 5/16 in | 17 | 14.9 ft | 19.6 ft |
| 144 in (12 ft) | 19 | 7 9/16 in | 18 | 15.8 ft | 20.9 ft |
Residential stair code at a glance (IRC R311.7)
| Rule | Limit |
|---|---|
| Riser height | 7.75 in maximum |
| Tread depth | 10 in minimum (plus a ¾–1¼ in nosing when under 11 in) |
| Riser and tread variation | No more than ⅜ in between the largest and smallest in a flight |
| Stair width | 36 in minimum |
| Headroom | 6 ft 8 in minimum |
| Rise of one flight | 151 in (12 ft 7 in) maximum, then a landing |
| Handrail | Required with 4 or more risers, 34–38 in above the nosings |
Local codes can be stricter, and decks follow the deck guide (AWC DCA 6) for stringers. Comfort rule of thumb: 2 × riser + tread ≈ 24–25 in.
Frequently asked questions
How do I calculate the number of stairs I need?
Measure the total rise from the finished lower floor (or ground) to the finished upper floor (or deck surface) in inches. Divide by 7.75 in and round up: that is the number of risers. Divide the total rise by that number for the exact riser height. You need one fewer tread than risers. For 108 in of rise: 108 ÷ 7.75 = 13.9, so 14 risers of 7 11/16 in and 13 treads.
What is the standard stair rise and run?
U.S. residential code (IRC) allows risers up to 7.75 in and treads at least 10 in deep. Most comfortable stairs land around a 7 to 7 ½ in riser with a 10 ½ to 11 in tread, which follows the rule 2 × riser + tread = 24 to 25 in.
How long is the total run of a staircase?
Total run = number of treads × tread depth. With 13 treads of 10 ½ in, the stairs run 136.5 in, about 11 ft 4 in, measured horizontally from the top nosing to the bottom riser.
How many stringers do I need?
Space cut stringers no more than 18 in apart for decks (AWC DCA 6), so a 36 in wide stair needs 3 stringers and a 48 in stair needs 4. Interior stairs with thick treads may allow wider spacing; check your code.
When do stairs need a landing?
When one flight would rise more than 151 in (12 ft 7 in), or where a door swings over the stairs. Landings must be at least as wide as the stairs and 36 in deep in the direction of travel.
Run a garden club, nursery or landscaping site? Embed this calculator free with one line of code.
Related free tools
Stair Stringer Calculator
Cut layout, stringer length, throat depth and how many stringers.
Open tool →Deck Calculator
Deck boards, joists, hangers, screws or clips and footing concrete.
Open tool →Board Foot Calculator
Board feet, linear feet and cost for a lumber list.
Open tool →Log Board Foot Calculator
Board feet in logs by Doyle, Scribner and International ¼ in.
Open tool →Sources and assumptions
Code limits from the 2021 International Residential Code, section R311.7; stringer spacing (18 in) and minimum throat (5 in) from the American Wood Council DCA 6 deck guide. Board depths are actual sizes (2×12 = 11 ¼ in). Your local code and inspector have the final say.