Remodelers

Staircase Calculator

Calculate riser height, tread depth, number of steps, and total run for code-compliant stairs.

Floor to floor measurement (9 ft = 108")
14
Risers
7.71"
Actual Riser Height
13
Treads
11.4 ft
Total Run
14.5 ft
Stringer Length
4
Stringers (2x12)
Passes IRC code
Code Check

108" total rise / 14 risers = 7.71" per riser. 13 treads at 10.5" = 11.4 ft total run. Riser + tread = 18.2" (comfort range is 17-18"). IRC limits: max riser 7.75", min tread 10", min width 36". All risers must be within 3/8" of each other.

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How to calculate stair dimensions

The two numbers that matter are rise and run. Rise is the total height from one floor to the next. Run is the horizontal distance each step covers. Divide the total rise by your target riser height (usually 7 to 7.75 inches) to get the number of steps. The number of treads is always one less than the number of risers because the top floor acts as the last step.

Building code requirements for stairs

Residential building codes typically require risers between 7 and 7.75 inches, treads at least 10 inches deep, and a minimum stairway width of 36 inches. Headroom needs to be at least 6 feet 8 inches. Riser heights cannot vary by more than 3/8 inch from step to step. Uneven risers are a trip hazard and an inspection fail. This calculator helps you hit code compliant dimensions from the start.

The 7-11 rule for comfortable stairs

The most comfortable stairs have a 7 inch rise and an 11 inch tread depth. This is the sweet spot that feels natural to walk up and down. If you increase the rise, you decrease the run, and vice versa. The old rule of thumb is that the rise plus the run should equal about 17 to 18 inches. Anything outside that range starts to feel awkward.

Common Questions

How wide do stairs need to be by code?

IRC code requires a minimum of 36 inches wide for residential stairs. That is measured between the finished walls or handrails. Most builders go 42 inches for a more comfortable stairway.

Do stairs need a landing?

Yes, if the staircase makes a turn. Code also requires a landing at the top and bottom that is at least as deep as the stairs are wide. A straight run under 12 feet does not need a mid-flight landing.

How much does it cost to build stairs?

A basic straight run interior staircase costs $1,000 to $2,500 in materials. Add $1,500 to $3,000 for labor. L-shaped or curved stairs cost significantly more because of the extra framing and custom cuts.

Can I change the number of steps in my stairs?

Only if the total rise stays the same. Adding or removing a step changes every riser height, and code says all risers must be within 3/8 inch of each other. You cannot just add a step without redoing the math.

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