Stair Stringer Calculator
Enter the rise and run to calculate the diagonal stringer length and the number of stringers you need.
Results
- Stringer length
- 169.01 in (14.08 ft)
- Total run
- 130 in
- Stringers needed
- 4
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
This calculator gives the stringer length, rise and run per step, and the cut layout you mark with a framing square.
It also accounts for dropping the bottom of the stringer by one tread thickness so the first step is not taller than the rest.
Also works as a stringer layout calculator, stair cut calculator, and stringer length estimator.
How to use the stair stringer calculator
- Enter the total rise in in.
- Enter the number of steps.
- Enter the tread depth in in.
- Enter the stair width in in.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Total rise
- 108 in
- Number of steps
- 14
- Tread depth
- 10 in
- Stair width
- 36 in
Results
- Stringer length
- 169.01 in (14.08 ft)
- Total run
- 130 in
- Stringers needed
- 4
Using the example values above, the stair stringer calculator returns 169.01 in (14.08 ft) (stringer length). Change any field to match your own project and the numbers update instantly.
Code limits worth checking
Residential code commonly caps riser height at 7.75 inches and requires a minimum 10 inch tread depth. Risers within a flight must not vary by more than 3/8 inch.
A useful check is that twice the rise plus the run should land between 24 and 25 inches for comfortable stairs.
Stringer spacing and material
Space stringers 16 inches on centre for 5/4 decking and 12 inches for composite treads. A 36 inch wide stair usually needs three stringers, and 48 inch needs four.
Cut stringers from 2 by 12 stock. After notching, at least 5 inches of solid material must remain behind the cuts or the stringer is structurally unsound.
Nominal vs actual (dry)
| Nominal | Actual |
|---|---|
| 1×4 | 3/4 × 3 1/2 in |
| 1×6 | 3/4 × 5 1/2 in |
| 2×4 | 1 1/2 × 3 1/2 in |
| 2×6 | 1 1/2 × 5 1/2 in |
| 2×8 | 1 1/2 × 7 1/4 in |
| 2×12 | 1 1/2 × 11 1/4 in |
Formula
Stringer length = √(total rise² + total run²). Use one stringer every ~16 in of stair width plus one.
Frequently asked questions
- How far apart should stair stringers be?
- Space stringers no more than 16 in on center for 5/4 treads, 12 in for heavier loads.
- What size lumber for stringers?
- Use 2×12 lumber so enough material remains after notching.
- How long does a stair stringer need to be?
- Stringer length is the square root of total rise squared plus total run squared. A 36 inch rise over 55 inch run gives a stringer about 66 inches long before cuts.
- How many stringers do I need?
- Three for stairs up to 36 inches wide, four up to 48 inches, spaced 16 inches on centre or 12 inches for composite treads.
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