Calculate the number of steps, rise, run, stringer length, and total staircase dimensions for any height. Results are checked against IRC building code requirements.
Stair dimensions IRC code checked
in
Measure from finished floor to finished floor
in
IRC minimum: 10 in | Comfortable: 11–12 in
in
IRC minimum: 36 in (3 ft)
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Steps
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Rise per step
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Run per step
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Stair angle
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Stringer length
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Horizontal run
Rise per step
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Run (tread) depth
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Comfort formula (2R+T)
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Number of steps—
Actual rise per step—
Tread depth (run)—
Total horizontal run—
Stringer length (each)—
Stringers needed—
Treads needed—
Risers needed (if closed)—
IRC stair code requirements
Rise (riser height)
Min: 4 in | Max: 7¾ in Max variation between steps: ⅜ in
Run (tread depth)
Min: 10 in | No max Nosing: ¾–1¼ in beyond riser
Stair width
Min: 36 in (residential) Commercial: 44 in minimum
Headroom
Min: 6 ft 8 in (80 in) Measured vertically above tread
Handrail height
34–38 in above tread nosing Required when 4+ risers
Comfort formula
2 × Rise + Run = 24–25 in Ideal comfort range
Frequently asked questions
How do I calculate stair rise and run? ›
Measure the total vertical height from finished floor to finished floor in inches. Divide by your desired riser height (7 inches is ideal) to get the number of steps — round to the nearest whole number. Then divide the total height by the number of steps to get the exact rise per step. The run (tread depth) is typically 10–12 inches. This calculator does all of this automatically and checks the result against building code.
What is the ideal rise and run for stairs? ›
The most comfortable stair dimensions use the "comfort formula": 2 × rise + run = 24 to 25 inches. A 7-inch rise + 11-inch run = 25 (ideal). A 7.5-inch rise + 10-inch run = 25 (acceptable). The IRC allows up to 7¾ inch rise and minimum 10 inch run, but lower, longer stairs are more comfortable for everyday use — especially for elderly people and young children.
How long does a stair stringer need to be? ›
Stringer length = √(total rise² + total run²) — the diagonal hypotenuse of the staircase. For a 10-step staircase with 7-inch rise and 11-inch run: total rise = 70 in, total run = 110 in, stringer = √(70² + 110²) = √(4900 + 12100) = √17000 ≈ 130 in (10.8 ft). Always buy the next standard lumber length above your calculated need.
How many stringers do I need? ›
Use 2 stringers for stairs up to 30 inches wide, 3 stringers for 30–48 inch wide stairs, and add one stringer for every additional 16 inches of width beyond that. Most residential stairs use 3 stringers (two outer + one center) for a 36-inch wide staircase. The center stringer prevents tread sag and bounce.
What lumber do I use for stair stringers? ›
2×12 lumber is the standard for cut stair stringers. It gives you the required 3.5 inch minimum remaining depth after cutting notches for the rise and run. For outdoor deck stairs, use pressure-treated 2×12. For indoor stairs, construction-grade Douglas fir or southern yellow pine are common choices. LSL (laminated strand lumber) is stronger and straighter than dimensional lumber and is a premium option for longer stringers.
About this stair calculator
This calculator uses the total rise to determine the optimal number of steps and exact rise per step, then calculates the stringer length (the diagonal hypotenuse), total horizontal run, tread count, and riser count. All results are automatically checked against IRC (International Residential Code) requirements for rise, run, and the comfort formula.
The interactive SVG diagram
The stair diagram updates in real time as you calculate, showing a scaled visual of your staircase with rise, run, and stringer dimensions labeled. This helps you visualize the final staircase and verify the proportions before cutting any lumber.