Stair Stringer Calculator
Calculate the number of risers, the exact riser height, the tread count, and the total horizontal run for a staircase from the total rise.
How to use this tool
- Measure the total rise from the lower finished floor to the upper finished floor.
- Enter a comfortable target riser height (about 7-7.75 in).
- Enter the tread depth (run per step), at least 10 in for most codes.
- Read the riser count and the exact riser height to cut.
- Confirm the total run fits your available floor space.
Lay out a safe, code-compliant staircase. Enter the floor-to-floor rise and your target riser and tread, and this tool gives you the riser count, exact riser height, tread count, and total run.
Formula
Pick a riser count that lands near the comfortable target height:
Risers = round( Total rise ÷ Target riser )
Actual riser height = Total rise ÷ Risers
There is always one fewer tread than riser (the top landing is not a tread):
Treads = Risers − 1
Total run = Treads × Tread depth
How it works
Designing a stair starts from the total rise — the vertical distance between the two finished floors. We divide it by a comfortable target riser height and round to the nearest whole number, because every riser in a flight must be the same height. Dividing the total rise back by that whole riser count gives the exact riser height to cut, which is what keeps the steps uniform and safe.
A staircase always has one fewer tread than riser: the floor at the top serves as the final landing, so the last riser steps up onto it rather than onto a tread. Multiplying the tread count by the tread depth (the run per step) gives the total horizontal run, which you need to confirm the stair fits the available floor space before cutting stringers.
Most building codes cap riser height near 7.75 inches and require a minimum tread depth around 10 inches; a common comfort guideline is that two risers plus one tread should total 24-25 inches. The calculator targets a comfortable riser, but always verify the result against your local code and adjust the target if the actual riser height lands too high or too low.
Worked example
108 in total rise, 7.5 in target riser, 10 in treads
- Risers = round(108 ÷ 7.5) = round(14.4) = 14 risers.
- Actual riser height = 108 ÷ 14 = 7.71 in (within code).
- Treads = 14 − 1 = 13 treads.
- Total run = 13 × 10 in = 130 in.
14 risers | Riser 7.71 in | 13 treads | Run 130.00 in
Riser count and height by total rise (7.5 in target)
| Total rise | Risers | Actual riser | Treads |
|---|---|---|---|
| 24" | 3 | 8.00" | 2 |
| 36" | 5 | 7.20" | 4 |
| 48" | 6 | 8.00" | 5 |
| 60" | 8 | 7.50" | 7 |
| 108" | 14 | 7.71" | 13 |
Key terms
- Rise
- The vertical height of one step (a single riser) or, as 'total rise', the full floor-to-floor height of the staircase.
- Riser
- The vertical face between two treads. Every riser in a flight should be the same height for safety.
- Tread
- The horizontal surface you step on. Its depth is the 'run' of each step. A flight has one fewer tread than riser.
- Stringer
- The sloped structural board, notched or routed, that supports the treads and risers along each side of the stair.
- Total run
- The total horizontal distance the staircase spans, equal to the number of treads times the tread depth.
Frequently asked questions
- How many stairs do I need for a given height?
- Divide the total floor-to-floor rise by a comfortable riser height (about 7.5 in) and round to the nearest whole number. A standard 108-inch rise gives 14 risers and 13 treads.
- What is a comfortable riser height?
- Around 7 to 7.75 inches. Most codes cap risers at about 7.75 inches, and a common comfort rule is that two risers plus one tread should total 24-25 inches.
- Why is there one fewer tread than riser?
- The upper floor acts as the final landing, so the top riser steps onto the floor instead of onto a tread. A flight therefore always has one more riser than tread.