Deck stairs calculator
Deck stair stringer calculator
Measure from the deck surface to the landing and get the steps: how many risers and how tall, the treads, how long each stringer is and what board to cut it from, and the one cut at the foot of the stringer that decides whether every step comes out the same height.
Enter your riseOptional
What will it cost?
Every material the calculator worked out gets its own price. Each field starts at a typical US figure so you have something to work from — change any of them to what your own supplier charges.
These prices are approximate. They are national US retail figures, and what you actually pay varies with your region, your supplier, the season and how much you buy at once. Treat them as a starting point, not a quote — always price the job from your own supplier's current figures before you order.
Your prices
More in this series
The rest of the deck
A deck is boards, frame, stairs, railing and finish. The sizes you have entered here carry across to the rest.
- Deck Material Calculator Deck boards by length, joists, beam, posts, hangers and screws or hidden clips
- Deck Stain Calculator Gallons of stain for the deck floor and every face of the railing
- Deck Railing and Post Spacing Calculator Railing posts, balusters under the 4 in rule, rails, brackets and screws
- Deck Footing Sizes and Spacing Form tube sizes, pad size by load and soil, and frost depth
- Deck Joist and Beam Span Tables Joist spans by species, size and spacing, beam spans, cantilevers and ledger fasteners
- Deck Board Sizes and Lengths Nominal and actual decking sizes, stock lengths, coverage and joist spacing
Based on your result
What you'll need
Cut one stringer, check it against the deck and the landing, then use it as the pattern for the rest.
- 2 × 12 stringers
- Pressure-treated, one per spacing across the width
- Calculate above
- Tread boards
- Cut to the stair width, two or three per tread
- —
- Riser boards and skirt
- Close each step face and cover the outer stringers, in the tread material
- —
- Stringer ties
- Two per stringer: one at the deck, one at the foot
- —
- Framing square with stair gauges
- Clamped at riser and tread to mark every step alike
- 1
- Landing
- A concrete pad or compacted gravel under the foot
- —
The maths
How this deck stringer calculator works
Every riser in a flight has to match — the code allows ⅜ in between the tallest and the shortest, because a foot that has taken two steps expects the third to be the same. The rise is divided into equal steps first, and everything else follows from that one number.
riser = total rise ÷ risers
treads = risers − 1
run = treads × tread depth
stringer = √((run + one tread)² + rise²)
stringers = ⌈ width ÷ spacing ⌉ + 1
- 01
Divide the rise
Total rise over the riser you would like, rounded to whole steps. If that leaves a riser over 7¾ in, one more step goes in.
- 02
Count the treads
The deck is the top step, so a flight has one tread fewer than it has risers.
- 03
Size the stringer
The diagonal of the run and the rise, plus one tread of run for the plumb cut at the top and the seat at the bottom — that sets the 2 × 12 to buy.
- 04
Drop the stringer
Treads sit on the cuts, so every step surface is one tread thickness higher than its cut. Taking that thickness off the foot of the stringer brings the bottom step back down and the top step back up to match.
- 05
Space the stringers
One at each edge and one every 12 or 16 in between, so no tread spans further than it can carry.
Good to know
Deck stair questions, answered
Four risers of 7½ in and three treads. At 11 in treads the flight runs 33 in out from the deck, and each stringer is cut from an 8 ft 2 × 12.
The diagonal of the total run and the total rise, plus one more tread of run to cover the plumb cut at the top and the level seat at the bottom. Buy the next standard length up; the calculator names it.
Sixteen inches on center is common for 5/4 wood treads, and many composite treads need 12 in. A 36 in wide stair at 16 in takes four stringers: one at each edge and two between.
The 2021 IRC sets 7¾ in as the most any riser may be, a 10 in minimum tread depth, and no more than ⅜ in between the tallest and shortest riser in a flight.
Because the treads sit on top of the stringer cuts. Every tread surface ends up one tread thickness above its cut, so unless the foot of the stringer is cut down by that thickness, the first step is taller and the top step shorter by the same amount — a 1 in tread makes them 2 in apart, far past the ⅜ in limit.
Usually once a flight has four or more risers, but the rule has exceptions and local amendments — check with the building department before you build.