Deck stairs
Deck stair & stringer calculator.
From the total rise, get the number of risers, the riser height, treads, total run, and the stringer length to cut. A 36 in high deck needs about 5 risers and a 55 in stringer.
36 in rise
5 risers
4 treads
Riser height
7.20 in
uniform, near 7.5 in
Stringer length
55.3 in
rise-run hypotenuse
Stairs by deck height
Risers and stringer length by total rise
Taller decks need more risers and longer stringers. These use a ~7.5 in target riser and a 10.5 in tread run. Keep every riser equal, and confirm the rise and run against your code.
| Total rise | Risers | Riser height | Stringer length |
|---|---|---|---|
| 24 in | 3 | 8.00 in | 31.9 in |
| 36 in | 5 | 7.20 in | 55.3 in |
| 48 in | 6 | 8.00 in | 71.1 in |
Wood or concrete?
This sizes wood stringers for a deck. For poured concrete steps, use the concrete stairs calculator to estimate volume and bags instead.
Formula shown
How the stair estimate works
1. Risers and riser height
risers = round(total rise / target riser); riser height = total rise / risers
2. Treads and total run
treads = risers - 1; total run = treads x tread run
3. Stringer length
stringer = sqrt(total rise^2 + total run^2)
Code controls the numbers
Local code typically caps riser height, sets a minimum tread depth, and requires uniform risers and a graspable handrail. Treat this as a starting layout and verify the final rise and run before cutting stringers.
Sources
- Decks.com stair stringer layout — riser, tread, and stringer layout method
- Stair geometry (rise/run) — stringer length as the hypotenuse of rise and run
Reviewed for estimating accuracy
Last updated: June 26, 2026
FAQ
Deck stair questions
Stair stringers, step count, riser height, tread depth, and stringer count for a deck.
How do I calculate stair stringers? + -
Divide the total rise by a comfortable riser height (about 7.5 in) and round to whole risers. The stringer length is the hypotenuse: the square root of total rise squared plus total run squared. For a 36 in rise, that is about 55 in.
How many steps do I need for my deck? + -
Steps follow the deck height. A 36 in high deck works out to about 5 risers and 4 treads at a ~7.2 in riser. Taller decks add steps. Pick the riser count that keeps each riser close to your target height.
What is a comfortable riser height and tread depth? + -
Many stairs use a riser near 7 to 7.5 in and a tread run around 10 to 11 in. Building codes commonly cap the riser around 7.75 in and set a minimum tread depth, and require risers to be uniform. Verify against your local code.
How many stringers do I need? + -
Stringers are spaced like joists, often 16 in on center. A typical 3 to 4 ft wide stair uses 3 to 4 stringers. Wider stairs and heavier loads need more; check the stringer spacing for your tread material.