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IRC R311
Validated against the standard.
PDF export
Pro-only. Generate professional reports.
$2.99 Pro
Lifetime unlock. No subscriptions.
How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact IRC R311 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Stairs have to be code-compliant and comfortable to climb. This app splits a total rise into equal risers and treads that satisfy IRC R311.7, and gives the stringer layout dimensions.
The IRC limits
- Maximum riser height — 7-3/4 inches.
- Minimum tread depth — 10 inches.
- Riser-to-riser and tread-to-tread may not vary by more than 3/8 inch across the flight.
- Many builders also check the comfort rule (rise + run ≈ 17 to 18 inches).
Worked example
A total rise of 109 inches ÷ 7.5 ≈ 14.5, so use 15 risers at 109 ÷ 15 = 7.27 inches each, with 14 treads. At a 10-inch run the total run is 140 inches — all within IRC limits.
Related calculators
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Stair FAQ
What are the IRC riser and tread limits?
The IRC allows a maximum riser height of 7-3/4 inches and requires a minimum tread depth of 10 inches, with no more than 3/8 inch variation between the largest and smallest in a flight.
How does it choose the number of risers?
It divides the total rise by the maximum riser, rounds up to a whole number of risers, then divides back to get an equal riser height within the limit.
Does it give stringer dimensions?
Yes — the riser height, tread run, total run, and the layout marks for cutting the stringer.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
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