Deck steps are not sold by the piece, so the work starts with the total rise: the height from the top of the decking straight down to the landing or the ground. The steps follow from that height and the tread depth you choose. For indoor and general stairs, the stair stringer calculator is the better fit.
How to use this calculator
- Measure the total rise straight down from the top of the decking to the landing or ground. On a slope, measure at the spot where the bottom step will stand, not under the deck edge. Enter it in feet or inches.
- Leave the maximum riser at 7.75 inches, or set a lower value for shorter steps.
- Enter the tread depth you plan to build, at or above 10 inches, the code minimum. Then check the total run against the space at the bottom.
- Read the risers, riser height and treads. Every riser comes out the same height, so cut each stringer to the same pattern.
Worked examples
Short deck step
Total rise: 24 in
- Risers
- 4 steps
- Riser height
- 6.00 in
- Treads
- 3
- Total run
- 30.0 in
- Stringer length
- 3.20 ft
- Stair angle
- 31.0°
Deck over a sloped yard
Total rise: 4 ft · Tread depth: 11 in
- Risers
- 7 steps
- Riser height
- 6.86 in
- Treads
- 6
- Total run
- 66.0 in
- Stringer length
- 6.80 ft
- Stair angle
- 31.9°
Tall deck with wide treads
Total rise: 6 ft · Tread depth: 12 in
- Risers
- 10 steps
- Riser height
- 7.20 in
- Treads
- 9
- Total run
- 108.0 in
- Stringer length
- 10.82 ft
- Stair angle
- 31.0°
Mid-height deck, lower risers
Total rise: 3 ft · Maximum riser height: 7 in
- Risers
- 6 steps
- Riser height
- 6.00 in
- Treads
- 5
- Total run
- 50.0 in
- Stringer length
- 5.13 ft
- Stair angle
- 31.0°
Total run for common deck heights and tread depths
| Deck height | Tread depth: 10 in | Tread depth: 12 in |
|---|---|---|
| 24 in | 30.0 | 36.0 |
| 36 in | 40.0 | 48.0 |
| 48 in | 60.0 | 72.0 |
| 60 in | 70.0 | 84.0 |
Each cell: Total run (in). Inputs not in the table use the calculator's starting values.
Measuring the total rise on a deck
The total rise runs from the top of the decking straight down to the surface where the bottom step lands. Measure it with a level and a tape, not along the stringer.
On a slope, the ground under the deck edge may sit higher or lower than the landing spot. Measure at the landing spot, and make sure it is firm and level. If the bottom step will sit on a concrete pad, use the concrete slab calculator for it.
How the calculation works
The calculator divides the total rise by the maximum riser and rounds up to a whole number of risers. Dividing the rise by that count gives an even riser height, which never exceeds the maximum.
Treads are the risers less the top step, since the deck surface has no tread of its own. The total run is the treads times the tread depth, which is how far the steps reach from the deck. The stringer length is the diagonal across the rise and the run, and the stair angle comes from the riser height and the tread depth.
Code limits, handrails and guards
The International Residential Code sets the limits the calculator starts from. A riser may be no taller than 7.75 inches, a tread at least 10 inches deep, and the largest difference between risers or treads in a flight is 0.375 inch. The stair must be at least 36 inches wide.
A handrail is needed on at least one side of a flight with 4 risers or more. Where an open side drops more than 30 inches to the floor or grade below, it needs a guard. For spindle spacing along a guard, use the deck spindle spacing calculator.
The calculator does not check these limits for you. Local codes can differ from these figures, and your building department decides what applies to your deck.
Mistakes to avoid
- Measuring to the joists instead of the top of the decking. The boards add height, so the real risers come out taller than shown.
- Ignoring a slope at the bottom. A landing lower than the spot you measured makes every riser taller than shown.
- Shortening the tread to fit a tight yard. A tread under 10 inches falls below the code minimum, so move the landing instead.
- Treating the result as a cut list. The calculator gives the rise, run and stringer length. It does not lay out notches or choose lumber.
How to build deck stairs, step by step
Start with the risers, riser height and run from the calculator. Mark the riser and tread on a stringer with a framing square, cut it, and test-fit it before cutting the rest. Fasten the stringers to the deck frame and set the bottom on a firm, level landing. Keep the stairs at least 36 inches wide. Then add the risers and treads, keeping any difference between them within 0.375 inch.
Common questions
How do I calculate stair stringers for a deck?
Divide the total rise by the maximum riser and round up to get the risers. Divide the rise by that count for the riser height, then multiply the treads, which are the risers less the top step, by the tread depth for the total run. The stringer length is the diagonal across the rise and the run.
Do deck steps need a handrail?
Stairs with 4 risers or more need a handrail on at least one side. Local codes can add requirements, so check with your building department.
When does a deck need a guard?
A guard is needed along an open side where the drop to the floor or grade below is more than 30 inches. Check the guard height and spindle gaps with your building department, since those rules are separate from the steps.
How long is a stairway with a given number of steps?
The length depends on your tread depth and your total rise. The treads are one fewer than the risers, and the total run is the treads times the tread depth. Enter your rise and tread depth in the calculator to get the run and the stringer length. A tread can be no shallower than 10 inches.
How high should a handrail be on deck stairs?
A handrail on stairs sits 34 to 38 inches above the nosings. If the open side also needs a guard, that guard must be at least 34 inches high. Check the details with your building department.
How many stringers do deck stairs need, and how far apart?
A stair at the minimum width of 36 inches needs at least 3 stringers if all are cut stringers, and wider stairs should keep stringers no farther apart than 18 inches. Cut them from lumber at least 12 inches deep (nominal). Five-quarter wood treads can span up to 18 inches, but composite treads follow the maker's own span rating.