Stair Calculator
Decking & Fencing · Updated July 2026
Enter your stair's total rise and desired step dimensions to find exactly how many risers, treads, and stringers you need — plus the total run and stringer board length.
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How do I calculate stair rise and run?
Measure the total vertical rise, then divide by your desired riser height (7–7.75 in is typical) to get the number of risers. Treads are one fewer than risers, and total run is treads × tread depth (10 in minimum is standard).
How to measure rise and run for stairs
Measure total rise with a level and tape from the finished lower floor straight up to the finished upper floor — not along the stairwell diagonal. Divide that by your target riser height to get the number of risers, then subtract one for the tread count. Most residential codes cap riser height around 7.75 in and require at least a 10 in tread run, so aim for 7–7.5 in risers for a comfortable, code-friendly climb.
How many stair stringers you need
Stringers are the diagonal 2x12 boards that treads and risers attach to. Two stringers handle stairs up to about 36 in wide; add roughly one more for every additional 24 in of width, and consider a third stringer even on narrower stairs if you're using tile or stone treads that add weight. Lay out the stringer with a framing square before cutting, and buy boards long enough to cover the full diagonal length plus a few inches of margin.
How to use this calculator
- 1Measure the total rise — the vertical height from the lower level to the upper level.
- 2Enter your desired riser height and tread depth (7.5 in and 10 in are common).
- 3Enter your stair width to get the number of stringers.
- 4Read your risers, treads, total run, and stringers needed.
Frequently asked questions
How many stringers do I need for stairs?
Use two stringers for stairs up to 36 in wide, and add one more for roughly every additional 24 in of width. Heavier loads or tile treads may need closer spacing.
What is a stair stringer?
A stair stringer is the diagonal supporting board — typically a 2x12 — that treads and risers attach to. Most residential stairs use two to three stringers depending on width and load.
What is the standard rise and run for stairs?
Most U.S. residential codes cap riser height at 7.75 inches and require a minimum tread run (depth) of 10 inches, though local codes vary — always confirm with your local building department before building.
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