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Stair Calculator

Enter your total rise and preferred riser height to get exact step count, riser height, total run, and stringer length.

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Results

Number of steps--
Actual riser height--
Total run--
Stringer length--

Estimates only.

How it works

The calculator divides your total rise by the ideal riser height, rounds to the nearest whole number of steps, then back-calculates the exact riser. Total run is (steps minus 1) times tread depth. Stringer length comes from the Pythagorean theorem on the rise and run triangle.

Formula: Steps = round(Total Rise / Ideal Riser). Actual Riser = Total Rise / Steps. Total Run = (Steps - 1) x Tread Depth. Stringer = sqrt(Rise² + Run²) / 12 (to convert inches to feet).

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FAQs

How do I calculate how many stairs I need?

Divide the total rise in inches by your target riser height (typically 7 inches), then round to the nearest whole number. For example, a 36-inch rise divided by 7 gives 5.14, which rounds to 5 steps.

What is the 7-11 rule for stairs?

The 7-11 rule is a common building guideline: risers should be no more than 7 inches tall and treads should be at least 11 inches deep. This ratio keeps staircase pitch comfortable and safe for most users.

What is the 25 rule for stairs?

Some codes reference a combined riser-plus-tread rule of 17 to 18 inches (riser + tread = 17-18 in) rather than 25. Always check your local building code for the exact allowable riser and tread dimensions.

How long of a stringer do I need for 7 steps?

Measure the total rise and total run for your staircase, then apply the Pythagorean theorem: stringer = sqrt(rise squared + run squared). A 42-inch rise with a 60-inch run gives a stringer of about 73 inches (6.1 ft).