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Stair Calculator

Calculate the number of risers, tread depth, total rise and run, and stringer length for any staircase from floor-to-floor height. Includes IRC 2021 code compliance check.

Staircase Measurements

Floor-to-floor height in inches (e.g., 9 ft = 108 in)

IRC min: 10 in; typical comfort: 10–11 in

IRC 2021 limits: riser 4–7¾ in max (§R311.7.5.1) · tread ≥ 10 in (§R311.7.5.2). Local codes may differ — verify with your AHJ.

02 Result
Steps
12 steps (11 treads)
7 in per riser
Total rise84 in (7.00 ft)
Riser height7 in
Tread depth10 in
Number of treads11
Total run110 in (9.17 ft)
Stringer length138.41 in (11.53 ft)

About This Calculator

Enter the total floor-to-floor height (in inches) and desired tread depth, and get an instant breakdown of step count, riser height, total staircase run, and stringer length — all cross-checked against IRC 2021 residential stair code requirements. Great for deck stairs, basement stairs, and porch steps.

How It Works

Step count = round(totalRise ÷ 7 in target riser). Riser height = totalRise ÷ numSteps (uniform risers). Treads = numSteps − 1 (attached-top stair). Total run = treads × treadDepth. Stringer length = √(totalRise² + totalRun²) (Pythagorean). IRC 2021 bounds: riser 4–7.75 in, tread ≥ 10 in.

The Formula

stringer = √(totalRise² + ((steps−1) × tread)²)

totalRise
floor-to-floor height (in)
steps
number of risers = round(totalRise ÷ 7)
tread
tread depth (in, min 10 in per IRC)

Frequently Asked Questions

What is the maximum riser height for residential stairs?
IRC 2021 §R311.7.5.1 sets a maximum riser height of 7¾ inches (7.75 in) and a minimum of 4 inches for residential stairs. This calculator warns (but does not block) results outside those bounds — you may be measuring an existing stair that pre-dates current code. Always verify with your local authority having jurisdiction (AHJ), as local amendments can differ from the model IRC.
What is the minimum tread depth per code?
IRC 2021 §R311.7.5.2 requires a minimum tread depth of 10 inches. This calculator enforces that minimum: entering a tread depth below 10 in produces an error. Individual local codes may be more restrictive.
Why does the calculator show treads = steps − 1?
An attached-top stair (the most common residential type) starts at the lower floor and ends when you step onto the upper floor — that last landing is not a separate tread. So a 12-step stair has 11 treads. A free-standing stair landing at a nosing on both ends would have 12 treads; adjust accordingly.
How do I measure total rise?
Measure the vertical distance from the finished floor surface of the lower level to the finished floor surface of the upper level (or deck surface), in inches. Include finished flooring thickness if it will be added after framing.

Estimates only. Coverage figures (sq ft/gallon, bag yield, BTU/sq ft) are industry rules of thumb with real-world variance. Verify quantities with your supplier before purchasing.