Stair Calculator
Unit:
A stair calculator determines the optimal number of steps, riser height, and tread depth for a given floor-to-floor height. Building codes specify maximum riser height (7.75" in the US) and minimum tread depth (10") to ensure safe, comfortable stairs.
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Tip: Consistency is crucial — all risers must be within 3/8" of each other per building code. An uneven step is a major trip hazard.
- 1Measure total rise: the vertical distance from one floor to the next
- 2Divide by ideal riser height (~7.5") to find number of steps
- 3Round to nearest whole number and recalculate exact riser height
- 4Use Blondel formula: 2R + T = 24–25" (R=riser, T=tread) for comfort
Floor-to-floor height: 9 ft (108 inches)=14 steps, 7.71" riser, 9.58" tread108/14 = 7.71" riser
Height: 8 ft (96 inches)=13 steps, 7.38" riser, 10.24" treadComfortable standard stair
| Measurement | Minimum | Maximum | Ideal |
|---|---|---|---|
| Riser height | 4" | 7.75" | 7"–7.5" |
| Tread depth | 10" | — | 10"–11" |
| Headroom | 6'8" | — | 7'0"+ |
| Stair width | 36" | — | 42"+ |
| Handrail height | 34" | 38" | 36" |
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Fun Fact
The Blondel formula (2R + T = 24–25") was developed by French architect François Blondel in 1672 and remains the gold standard for comfortable stair design — 350 years later.
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