Free Stair Calculator
Work out riser height, tread count and total run for a staircase, with a check against IRC limits. Free, fast, and works entirely in your browser with no sign-up required.
Updated
Stair layout
IRC allows a maximum of 7.75 in.
IRC requires a minimum of 10 in.
Number of risers
15
risers
- Actual riser height
- 7.200in
- Number of treads
- 14treads
- Total run (horizontal)
- 140.00in
- Meets IRC riser/tread limits
- 1(1 = yes)
How this is calculated
risers = round(total rise ÷ target riser); actual riser = total rise ÷ risers; treads = risers − 1
- Riser count is rounded to a whole number and the rise divided evenly — an uneven last step is both a trip hazard and a code violation.
- IRC R311.7 caps residential risers at 7.75 in and requires treads of at least 10 in. "Meets IRC limits" reports 0 when your inputs breach either.
- Local codes and commercial stairs differ — confirm against the code your inspector uses.
- Tread depth excludes nosing overhang.
Frequently Asked Questions
How does the Stair Calculator work?
It applies the formula risers = round(total rise ÷ target riser); actual riser = total rise ÷ risers; treads = risers − 1. Enter your measurements and the result updates instantly in your browser — nothing is uploaded and no sign-up is needed.
Why should I include a waste allowance?
Offcuts, spillage, breakage and an uneven sub-base all consume material that the raw geometry does not account for. The default allowance is deliberately modest; increase it for complex layouts, and remember that running short usually costs more in a second delivery than the surplus did.
Are the results exact?
They are a close estimate, not a guarantee. Riser count is rounded to a whole number and the rise divided evenly — an uneven last step is both a trip hazard and a code violation. Real materials vary by supplier, moisture content and compaction, so confirm the rate with your supplier before placing a large order.
Is this tool free?
Yes, completely free with no registration. All calculations happen client-side in your browser.
Does it work on mobile?
Yes. The calculator is fully responsive and works on phones and tablets in any modern browser — useful when you are measuring on site.
Related Tools
Free Concrete Calculator
Work out how much concrete a slab needs in cubic yards, cubic feet and 60 or 80 lb bags. Free, fast, and works entirely in your browser with no sign-up required.
Free Roofing Calculator
Estimate roofing squares, shingle bundles and true roof area from your footprint and pitch. Free, fast, and works entirely in your browser with no sign-up required.
Free Age Calculator Online
Calculate your exact age in years, months, and days with zodiac signs. Free, fast, and works entirely in your browser with no sign-up required.
Free Percentage Calculator
Calculate percentages easily with multiple calculation modes. Free, fast, and works entirely in your browser with no sign-up required.
About the Stair Calculator
The Stair Calculator divides a total floor-to-floor rise into equal whole risers, then reports the resulting riser height, tread count and total horizontal run — and flags when the layout would breach IRC limits. Enter your measurements and the result updates as you type — there is nothing to submit and nothing to wait for.
Everything runs in your browser. Nothing you enter is sent to a server, there is no sign-up, and there is no usage limit.
Who it's for
Anyone framing stairs for a deck, basement or loft, and inspectors sanity-checking a design.
How the calculation works
risers = round(total rise ÷ target riser); actual riser = total rise ÷ risers; treads = risers − 1
The result depends on a few standard constants, which are stated on the page rather than hidden:
- Riser count is rounded to a whole number and the rise divided evenly — an uneven last step is both a trip hazard and a code violation.
- IRC R311.7 caps residential risers at 7.75 in and requires treads of at least 10 in. "Meets IRC limits" reports 0 when your inputs breach either.
- Local codes and commercial stairs differ — confirm against the code your inspector uses.
- Tread depth excludes nosing overhang.
Getting an accurate estimate
Measure twice. Small errors in a linear dimension compound, because material volume scales with two or three of them at once — a 6-inch error across a 20-foot run is over a cubic foot of material on a 4-inch pour.
Keep the waste allowance. The default is deliberately conservative: offcuts, spillage, uneven sub-base and breakage are all real, and running short mid-job usually costs more in a second delivery than the surplus did.
Round up when you order. Suppliers sell in fixed increments — quarter yards, whole bags, full boxes — so treat the figure here as the minimum you need rather than the exact amount to buy.