Stair Calculator
Turn a floor-to-floor height into riser, run, and stringer dimensions — with a scaled diagram and code checks.
Suggested for a ~7″ riser: risers.
Enter a total rise above zero, at least 2 risers, and a tread depth to see results.
Riser height — each step
″ · cm
″ rise ÷ risers = ″ each · treads × ″ = ″ run ✓
Common staircases, already worked out
Each link opens the calculator pre-filled. All use a 10″ tread depth.
Stair dimensions and building code
What is a comfortable stair riser height?
Around 7 inches is the sweet spot for most homes. Residential building code (IRC R311.7) allows a maximum riser of 7 3/4 inches. Lower risers feel easier underfoot but add steps and lengthen the staircase. This calculator divides your total rise evenly so every riser is identical, which code requires.
How many steps do I need for a 9-foot floor-to-floor height?
A 9-foot rise is 108 inches. Dividing by a target 7-inch riser gives about 15 risers, which works out to 7.2 inches each — comfortably under the code maximum. That flight has 14 treads. Enter your exact rise above and the calculator picks a sensible riser count you can fine-tune.
What is the maximum riser height allowed by code?
The International Residential Code sets the maximum riser at 7 3/4 inches. It also requires that the tallest and shortest riser in a flight differ by no more than 3/8 inch. Local codes can be stricter, so confirm with your building department before you cut stringers.
What is the minimum tread depth?
Residential code requires a minimum tread depth of 10 inches, measured from nosing to nosing. Deeper treads of 11 or 12 inches feel more comfortable, especially on a long flight, but each extra inch of tread adds to the total run and the floor space the staircase consumes.
How do I calculate stringer length?
The stringer is the diagonal of the staircase. Its length is the square root of the total rise squared plus the total run squared. For a 108-inch rise and a 140-inch run, that is the square root of (108² + 140²) ≈ 176.8 inches. Buy stringer stock a little longer to allow for the cuts at the top and bottom.
What is the "2R + T" comfort rule?
A long-standing rule of thumb says two riser heights plus one tread depth should total 24 to 25 inches. It keeps the relationship between step height and step depth comfortable for an average stride. The calculator shows your 2R + T figure and flags it if it falls outside that range.
Why must every riser be the same height?
People climb stairs without looking, their feet expecting each step to be identical. A single riser that is even 1/2 inch off is a trip hazard, which is why code limits the variation to 3/8 inch across a flight. Always divide the total rise into equal risers — never leave the odd inches in the last step.