justyourcalculatorStair Calculator
Steps, riser height, stringer length and angle, checked against the IRC code.
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Stair Calculator
Steps, rise, run, stringer length and code check
Steps
14 risers, 13 treads
Each step 7.71 in high and 10 in deep
- Riser height
- 7.71 in
- Tread depth
- 10 in
- Total run
- 130 in (10 ft 10 in)
- Stringer lengthAlong the slope, before trimming
- 169.01 in (14 ft 1.01 in)
- Stair angle30° to 37° feels most comfortable
- 37.6°
IRC code check: passes
- Riser ≤ 7.75 inYours: 7.71 in
- Pass
- Tread ≥ 10 inYours: 10 in
- Pass
- Width ≥ 36 inYours: 36 in (3 ft 0 in)
- Pass
- Comfort: 2 × riser + treadYours: 25.43 in (2 ft 1.43 in)
- Good
Limits from the 2021 International Residential Code (R311.7): risers at most 7¾ in, treads at least 10 in, width at least 36 in, headroom at least 6 ft 8 in, and a handrail 34 to 38 in high. Local codes can differ; check with your building department.
How it was calculated
- Risers = ⌈108 ÷ 7.75⌉ = 14
- Riser = 108 ÷ 14 = 7.714 in
- Total run = 13 treads × 10 in = 130 in
- Stringer = √(108² + 130²) = 169.01 in
- Angle = atan(7.714 ÷ 10) = 37.6°
| Step | Height from floor | Distance from first riser |
|---|---|---|
| 1 | 7.71 in | 0 in |
| 2 | 15.43 in | 10 in |
| 3 | 23.14 in | 20 in |
| 4 | 30.86 in (2 ft 6.86 in) | 30 in (2 ft 6 in) |
| 5 | 38.57 in (3 ft 2.57 in) | 40 in (3 ft 4 in) |
| 6 | 46.29 in (3 ft 10.29 in) | 50 in (4 ft 2 in) |
| 7 | 54 in (4 ft 6 in) | 60 in (5 ft 0 in) |
| 8 | 61.71 in (5 ft 1.71 in) | 70 in (5 ft 10 in) |
| 9 | 69.43 in (5 ft 9.43 in) | 80 in (6 ft 8 in) |
| 10 | 77.14 in (6 ft 5.14 in) | 90 in (7 ft 6 in) |
| 11 | 84.86 in (7 ft 0.86 in) | 100 in (8 ft 4 in) |
| 12 | 92.57 in (7 ft 8.57 in) | 110 in (9 ft 2 in) |
| 13 | 100.29 in (8 ft 4.29 in) | 120 in (10 ft 0 in) |
| 14 (top floor) | 108 in (9 ft 0 in) | 130 in (10 ft 10 in) |
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How the stair calculator works
Start from the total rise, the vertical distance from finished floor to finished floor. Dividing it by the tallest step you allow (7¾ in under the IRC) and rounding up gives the number of risers; the actual riser height is the total rise divided by that number.
A straight stair has one fewer tread than risers because the top floor acts as the last step. Total run = treads × tread depth, and the stringer length is the diagonal: √(rise² + run²). The angle is atan(riser ÷ tread).
A common comfort rule is 2 × riser + tread between 24 and 25 inches. For example a 7.5 in riser with a 10 in tread gives 25 in.
Using and checking your result
Published by JustYourCalculator. Check the units and assumptions above, and compare a known example before relying on the output. Calculations use browser arithmetic and may round displayed values.
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