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CalcSpectrum

Stair Calculator

Estimate stair riser count, riser height, tread depth, total run, and stringer length from total vertical rise, using IRC reference values.

Free to use · Instant results

Calculator Inputs

Total vertical height the stairs must climb, floor to floor. Must be a positive number.

Unit for the total vertical rise value above.

Number of Risers
14
Actual Riser Height
7.71
Number of Treads
13
Tread Depth
10.00
Total Run
130.00
Stringer Length
169.01
Stair Angle
39.72
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About these results

CalcSpectrum calculators produce automated estimates using established formulas and the specific values you enter. Because real-world outcomes depend on input accuracy, mathematical assumptions, and rounding conventions, please verify critical figures with an appropriately qualified financial, tax, medical, legal, or other professional, as relevant.

How It's Calculated

Formula

numberOfRisers=⌈totalRise7.75⌉actualRiserHeight=totalRisenumberOfRiserstotalRun=(numberOfRisers−1)×10stringerLength=totalRise2+totalRun2\text{numberOfRisers} = \lceil \dfrac{\text{totalRise}}{7.75} \rceil \\ \text{actualRiserHeight} = \dfrac{\text{totalRise}}{\text{numberOfRisers}} \\ \text{totalRun} = (\text{numberOfRisers} - 1) \times 10 \\ \text{stringerLength} = \sqrt{\text{totalRise}^2 + \text{totalRun}^2}

This calculator estimates basic stair geometry from a single input: the total vertical rise (floor-to-floor height) the stairs need to climb. It uses the IRC (International Residential Code) reference values of a 7.75 in maximum riser height and a 10 in minimum tread depth (stable across recent IRC editions) as design targets — the number of risers is the smallest whole count that keeps every riser at or under 7.75 in, and the total rise is then split evenly across that many risers to get the actual riser height. Tread depth is reported at the 10 in IRC minimum. This is a DESIGN ESTIMATE, not a code-compliance certification: actual local building code adoption and amendments vary by jurisdiction, so verify final dimensions against your local building department before construction.

Worked Examples

108 in total rise

  1. Number of risers = ceil(108 / 7.75) = ceil(13.94) = 14
  2. Actual riser height = 108 / 14 = 7.714 in
  3. Number of treads = 14 - 1 = 13
  4. Total run = 13 x 10 = 130 in
  5. Stringer length = sqrt(108^2 + 130^2) = 169.01 in

Frequently Asked Questions

Is this stair design guaranteed to meet my local building code?

No. This calculator uses the IRC's commonly cited maximum riser height (7.75 in) and minimum tread depth (10 in) as design reference values, but it does not verify compliance with any specific jurisdiction's adopted code edition or amendments. Always confirm final dimensions with your local building department.

Why does the actual riser height come out uneven, like 7.714 in?

The total rise rarely divides evenly by the maximum riser height, so this calculator rounds the riser count UP to the smallest whole number that keeps each riser at or under 7.75 in, then splits the total rise evenly across that many risers — every riser in a real staircase should be the same height.

Why is tread depth always 10 in regardless of my input?

This calculator's only input is total vertical rise, so tread depth is reported at the IRC minimum reference value (10 in) rather than computed from a run input you didn't provide.