Number of Steps
5
Actual Riser
7.20"
Stringer Length
55.3"
Angle
40.6°
Vertical height from floor to floor
Actual Riser
7.20"
Stringer Length
55.3"
Total Run
42.0"
Angle
40.6°
Inputs
Result
Risers = round(36 / 7.5) = 5 steps. Actual riser = 36 / 5 = 7.20". Treads = 5 - 1 = 4. Total run = 4 × 10.5 = 42". Stringer = sqrt(36² + 42²) = sqrt(3060) = 55.3". Angle = atan(36/42) = 40.6°.
Inputs
Result
Risers = round(108 / 7) = 15 steps. Actual riser = 108 / 15 = 7.20". Treads = 15 - 1 = 14. Total run = 14 × 11 = 154". Stringer = sqrt(108² + 154²) = sqrt(35380) = 188.10". Angle = atan(108/154) = 35.0°.
A stringer is the structural support board (usually 2x12) that runs diagonally along each side of stairs. It's cut in a saw-tooth pattern where treads (horizontal) and risers (vertical) attach. Most stairs have 2-3 stringers for support.
| Stair Width | Stringers Needed | Stringer Spacing |
|---|---|---|
| Up to 36" | 2 | At edges |
| 36" to 48" | 3 | 18-24" apart |
| 48" to 72" | 4 | 16-18" apart |
| Over 72" | 5+ | Max 16" apart |
IRC Residential Code: Max riser 7¾", min tread 10", max variation 3/8" between steps. Min width 36", headroom 6'8". Handrail required if 4+ risers. Commercial codes are stricter (7" max riser, 11" min tread).
| Requirement | Residential (IRC) | Commercial (IBC) |
|---|---|---|
| Max riser height | 7¾" (7.75") | 7" |
| Min tread depth | 10" | 11" |
| Min stair width | 36" | 44" |
| Max riser variation | 3/8" | 3/8" |
| Min headroom | 6'8" | 6'8" |
| Handrail height | 34-38" | 34-38" |
The "rule of 17-18": Rise + Run should equal 17-18 inches for comfortable stairs. Common combinations: 7" rise / 11" run (total 18"), 7.5" rise / 10" run (total 17.5"). Steeper stairs feel tiring; shallow stairs feel awkward.
| Rise | Run | Total | Feel |
|---|---|---|---|
| 6" | 12" | 18" | Shallow, easy (long stairs) |
| 7" | 11" | 18" | Ideal for most people |
| 7.5" | 10" | 17.5" | Standard residential |
| 7.75" | 10" | 17.75" | Code maximum, feels steep |
| 8" | 9" | 17" | Too steep, uncomfortable |
Number of risers = Total rise ÷ Target riser height. Then treads = Risers - 1 (top tread is the landing). Stringer length = √(Total rise² + Total run²). Example: 36" rise, 7.2" per step = 5 risers, 4 treads.
| Total Rise | Risers (at 7") | Treads | Total Run (10" treads) |
|---|---|---|---|
| 28" | 4 | 3 | 30" |
| 35" | 5 | 4 | 40" |
| 42" | 6 | 5 | 50" |
| 56" | 8 | 7 | 70" |
| 84" | 12 | 11 | 110" |
Stringer length = √(total rise² + total run²) + 12". A deck 42" high with 6 steps needs: √(42² + 60²) + 12" = 73" + 12" = 85" minimum. Use a 10' 2x12 to have extra for cutting and the bottom plumb cut.
| Deck Height | Steps | Run (10" treads) | Min Stringer Length |
|---|---|---|---|
| 24" | 4 | 30" | 4' (48") |
| 36" | 5 | 40" | 5' (60") |
| 48" | 7 | 60" | 7' (84") |
| 72" | 10 | 90" | 10' (120") |
| 96" | 14 | 130" | 14' (168") |
Use a framing square with stair gauges set to rise and run. Mark the first step at one end, then walk the square down the board for each step. Cut with circular saw, finish corners with handsaw. Always verify measurements before cutting.
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Last Updated: Feb 12, 2026
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