Stair Stringer Calculator
Find the number of steps, exact riser height, total run and cut length of a stair stringer from your floor-to-floor rise.
in
in
in
Passes the 2R+T comfort rule
- 1
Step count
108 ÷ 7 = 15Rounded to the nearest whole number — all risers must be equal. - 2
Total run
(15 − 1) × 10 = 140 - 3
Stringer length
√(108² + 140²) = 176.82 - 4
Riser height
108 ÷ 15 = 7.20
How does this calculator work?
Divide your floor-to-floor rise by about 7 in and round to get the step count, then divide the rise by that count for the equal riser height. Total run is (steps − 1) × tread depth, and the stringer length is the hypotenuse of rise and run. Check that 2 × riser + tread lands near 24–25 in.
Formula
How this is calculated
Enter the total rise (the vertical distance from one finished floor to the next), your chosen tread depth (the horizontal run of each step, typically 10–11 in / 254–279 mm), and a target riser height (about 7 in / 178 mm is most comfortable). The calculator divides the total rise by the target riser and rounds to a whole number of steps, because risers must all be equal.
The actual riser height is then the total rise divided by that step count. A flight has one fewer tread than risers (the top step lands on the upper floor), so total run equals (steps − 1) × tread depth. The stringer is the diagonal board the steps cut into, so its length is the hypotenuse √(totalRise² + totalRun²). The stair angle is atan(totalRise / totalRun).
Comfort is checked with the classic 2R + T rule: twice the riser plus the tread depth should fall between about 24 and 25 in (610–635 mm). Values outside that range tend to feel steep or stretched. All inputs share the same length unit (inches shown by default; substitute mm or cm consistently). Edge cases: zero or negative inputs return no result, and a single-riser flight has zero treads and zero run.
Frequently asked questions
About 7 in (178 mm) is the most comfortable and is widely used in residential code. The calculator rounds the step count so every riser ends up equal, which is what building inspectors require.
It is a comfort formula: twice the riser height plus the tread depth should total roughly 24–25 in (610–635 mm). It balances the step rise against its depth so the stair neither feels too steep nor too shallow.
The topmost riser brings you level with the upper floor, so that last step has no separate tread. A flight therefore has one fewer tread than it has risers.
Also known as
TG we-Calculate Editorial Team. (2026). Stair Stringer Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/stair-stringer-calculator
TG we-Calculate Editorial Team. "Stair Stringer Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/stair-stringer-calculator.
TG we-Calculate Editorial Team, "Stair Stringer Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/stair-stringer-calculator
@misc{wecalculate_stair_stringer_calculator, title = {Stair Stringer Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/stair-stringer-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?