Stair calculator
Number of steps, riser height, tread run and stringer length from your total rise, checked against the IRC limits.
You need
14 risers of 7 11/16 in
- Treads
- 13
- Total run
- 10 ft 10 in
- Stringer length
- 14 ft 1 in
- Stair angle
- 39.7°
- Shortest stringer board
- 16 ft
Riser height is 7.714 in exactly. The top floor or deck counts as the last step, so there's one fewer tread than risers.
Dimension check
- Riser height 7 11/16 in: within the IRC maximum of 7 3/4 in
- Tread depth 10 in: at or above the IRC minimum of 10 in
- Width 36 in: at or above the IRC minimum of 36 in
- Handrail required (4 or more risers), 34 to 38 in above the tread nosings
- Guards required on open sides (total rise over 30 in), at least 34 in high
- Keep at least 6 ft 8 in of headroom above the stairs, measured straight up from the line of the nosings.
Checks these dimensions against the model International Residential Code (IRC) R311.7 and R312.1 only. Your local code may differ and covers more (landings, nosings, lighting), so check with your building department and a qualified professional before you build.
How to calculate stair rise and run
Every riser in a flight should be the same height, so the calculator divides the total rise into the fewest equal risers that stay at or under your maximum.
- Risers = total rise ÷ maximum riser height, rounded up to a whole number
- Riser height = total rise ÷ risers
- Treads = risers − 1 (the upper floor is the last step)
- Total run = treads × tread depth
- Stringer length = √(total rise² + total run²)
Worked example
A 108 inch rise (9 ft 0 in) with a 7 3/4 in maximum: 108 ÷ 7.75 = 13.94, rounded up to 14 risers of 108 ÷ 14 = 7.714 in (about 7 11/16 in). That's 13 treads × 10 in = 130 in of run, and a stringer line of √(108² + 130²) = 169.0 in (14 ft 1 in).
How many steps for your stair height
Risers at the IRC maximum of 7 3/4 in and 10 inch treads. Use the calculator above for other choices.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 24 in (2 ft 0 in) | 4 | 6 in | 3 | 2 ft 6 in |
| 30 in (2 ft 6 in) | 4 | 7 1/2 in | 3 | 2 ft 6 in |
| 36 in (3 ft 0 in) | 5 | 7 3/16 in | 4 | 3 ft 4 in |
| 48 in (4 ft 0 in) | 7 | 6 7/8 in | 6 | 5 ft 0 in |
| 72 in (6 ft 0 in) | 10 | 7 3/16 in | 9 | 7 ft 6 in |
| 96 in (8 ft 0 in) | 13 | 7 3/8 in | 12 | 10 ft 0 in |
| 102 in (8 ft 6 in) | 14 | 7 5/16 in | 13 | 10 ft 10 in |
| 108 in (9 ft 0 in) | 14 | 7 11/16 in | 13 | 10 ft 10 in |
| 114 in (9 ft 6 in) | 15 | 7 5/8 in | 14 | 11 ft 8 in |
| 120 in (10 ft 0 in) | 16 | 7 1/2 in | 15 | 12 ft 6 in |
Residential stair limits
From the International Residential Code (IRC) R311.7 and R312.1. Many jurisdictions amend these, so confirm with your building department.
| Dimension | Limit |
|---|---|
| Riser height | 7 3/4 in maximum |
| Tread depth | 10 in minimum |
| Difference within a flight | 3/8 in maximum between the tallest and shortest riser, and between the deepest and shallowest tread |
| Width | 36 in minimum clear width |
| Headroom | 6 ft 8 in minimum |
| Handrail | Required on one side with 4 or more risers; 34 to 38 in above the nosings |
| Guards | On open sides where the total rise is over 30 in; at least 34 in high along the stair |
Stair questions
How many steps are in a flight of stairs?
It depends on the height between floors. With risers at the IRC maximum of 7 3/4 in, a 108 inch (9 ft 0 in) floor-to-floor rise needs 14 risers and 13 treads. The table above covers other heights.
What is the standard stair rise and run?
The IRC sets the limits for homes: risers no taller than 7 3/4 in and treads no shallower than 10 in. Shorter risers with deeper treads make an easier stair but take more floor space; try the "Gentler stairs" button above to compare.
How do I calculate stair stringer length?
Use the total rise and total run: stringer length = √(rise² + run²). For the example above that's 14 ft 1 in. That's the line length; buy a board long enough for the cuts at the top and bottom, which is why the calculator suggests the shortest standard length that covers it.
What height should a stair handrail or railing be?
Under the IRC, a handrail is required on at least one side of a flight with 4 or more risers, 34 to 38 inches above the tread nosings. Where the stair's open side is more than 30 inches above the floor or ground, it also needs a guard at least 34 inches high.
How do I measure the total rise?
Measure straight down from the finished surface at the top (floor or deck) to the finished surface where the bottom step will land, including any flooring still to be installed. For deck stairs on sloping ground, measure at the spot where the bottom step will sit.
How do I build deck stairs?
Work out the layout here first: enter the height from the deck surface to the landing spot, then mark the riser height and tread depth on each stringer with a framing square. Exterior stairs follow the same IRC limits; your local code may add requirements for footings, landings and guards, so check before you build.