Calculators / Fences and decks
Deck stair calculator: how many steps?
Measure from the top of the deck to where the stairs land. You'll get the risers, the treads, how far the stairs run out and how long to cut the stringers.
Updated · How we check our numbers
Build it like this
4 risers at 7½ in
3 treads at 10½ in, running out 2 ft 8 in. Each stringer is 3 ft 8 in on the slope, so buy 8 ft 2x12s.
- Risers
- 47½ in each
- Treads
- 310½ in each
- Total run
- 2 ft 8 in31½ in
- Stringer
- 3 ft 8 in8 ft 2x12
- Stringers
- 448 in wide
Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.
risers = 30 in ÷ 7.75 in max = 3.9, rounded up = 4
riser height = 30 in ÷ 4 = 7.50 in
treads = 4 risers − 1 (the deck is the top step) = 3
total run = 3 × 10½ in = 31½ in
stringer = √(30² + 31½²) = 43.5 in
bottom riser on the stringer = 7.50 − 1 in tread = 6.50 in
stringers = 48 in ÷ 18 in o.c., rounded up, + 1 = 4
Step counts for your rise
30 in total- 3 risers, 2 treads10 in rise, 1 ft 9 in run, stringer 3 ft 1 in2¼ in too tall
- 4 risers, 3 treads7½ in rise, 2 ft 8 in run, stringer 3 ft 8 inYours
- 5 risers, 4 treads6 in rise, 3 ft 6 in run, stringer 4 ft 4 inGentler
- 6 risers, 5 treads5 in rise, 4 ft 5 in run, stringer 5 ftGentler
IRC R311.7: risers 7¾ in max, treads 10 in min.
Cut the bottom riser on the stringer 6½ in tall, not 7½. The tread adds 1 in back. Skip this and the first step comes out tall.
Code wants every riser within 3/8 in of the others, and every tread too. Measure the rise at the spot the stairs will land, not at the house.
4 risers needs a handrail on at least one side. Top of the rail goes 34 to 38 in above the nosings.
Under 11 in of tread, each one needs a 3/4 to 1 1/4 in nosing past the riser below. Or skip the nosing and make the treads 11 in.
Land the stairs on something solid and level, like a concrete pad or compacted gravel. It needs to be as wide as the stairs and 36 in deep.
Hang the stringers off the rim with metal stair stringer connectors, not just toe screws.
See stringer connectors on Amazon (opens Amazon in a new tab)As an Amazon Associate we earn from qualifying purchases.
How we work it out
We split the total rise into the fewest risers that stay at 7 3/4 in or under, the IRC max. The deck itself is the top step, so you get one less tread than risers.
risers = total rise ÷ 7.75, rounded up
riser height = total rise ÷ risers
total run = (risers − 1) × tread depth
stringer = √(total rise² + total run²)
Treads under 10 in fail, and so do risers over 7 3/4 in if you pick your own count. One flight can only climb 12 ft 7 in before it needs a landing. Stairs need 36 in of width.
Cut stringers go 18 in on center at most, so we count one per 18 in of width plus one, and never fewer than 3. A cut 2x12 can span 6 ft level in any species. Past that, it needs a post under the middle.
Cut the bottom riser short by the thickness of one tread. Once the boards go on, every step comes out the same height.
Where the numbers come from
Check the grade
Price the deck
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