Stair Calculator
Calculate rise, run, riser height, tread count, stringer length, and stair angle — with live IRC code-compliance checks for residential stairs.
Code and structural values are preliminary — always verify with your local building official or a licensed engineer before building.
Amber items are comfort/advisory guidance, not pass/fail code requirements.
How to Calculate a Staircase
Start with the total rise — the finished floor-to-floor height. Divide it by a comfortable target riser (around 7–7.5 inches) and round to the nearest whole number to get your number of risers. Dividing the total rise by that count gives the actual riser height, keeping every step exactly equal. The number of treads is always one less than the number of risers, and the total run is the tread depth multiplied by the number of treads.
The stringer length is the diagonal of the rise-and-run triangle, found with the Pythagorean theorem, and the stair angle is the arctangent of rise over run. The IRC limits residential risers to a maximum of 7-3/4 inches and treads to a minimum of 10 inches, which this calculator checks live. These results are a planning aid — confirm dimensions, headroom, and handrail requirements with your local building official.
Frequently Asked Questions
What is the maximum stair riser height?
Under the International Residential Code (IRC), the maximum riser height for stairs is 7-3/4 inches (7.75"). The minimum tread depth is 10 inches. The greatest riser within any flight may not exceed the smallest by more than 3/8 inch.
How many steps for an 8-foot ceiling?
An 8-foot ceiling with floor framing gives roughly 105–109 inches of total rise. At about 7.5 inches per riser that works out to 14 risers (and 13 treads), with an actual riser height near 7.5–7.8 inches. Enter your exact floor-to-floor height above for precise numbers.
What is the 7-11 rule for stairs?
The "7-11 rule" is a comfort guideline: a roughly 7-inch riser paired with an 11-inch tread produces a comfortable, walkable stair. It pairs with the "2 × riser + tread = 24–25 inches" rule of thumb. The IRC code limits are a 7-3/4 inch max riser and 10-inch min tread.
Turn Your Measurements Into a Real Floor Plan
Once you know your dimensions, generate a labeled, to-scale floor plan in seconds — then export it to DXF or build it in 3D. No CAD experience needed.
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