How to use it for a deck
- Measure the total rise from the top of the finished decking to the top of the landing where the bottom step will sit. Measure at that exact spot, not under the rim joist. The total rise guide shows how.
- Enter it as the total rise. The form starts at 42 in as an example.
- Set the tread thickness. A 5/4 deck board is 1 in thick; 2× lumber is 1½ in. This shortens the first riser cut so every finished step comes out equal.
- Check the messages under the results. IRC limits are flagged as issues, and a throat under 5 in is flagged as a note, since trade guidance asks for more uncut wood on deck stringers.
- Open the Plans tab for the side profile, the stringer layout and the tread cut list.
Steps for common deck heights
This table shows the fewest risers that keep each riser at 7¾ in or less, with 10½ in treads. The deck surface counts as the top step, so there is one fewer tread than risers. The calculator rounds to the number of risers closest to the riser height you enter, so with a 7 in target it may suggest one more step on taller decks, which is more comfortable.
| Deck height | Risers | Riser height | Total run |
|---|
| 12 in | 2 | 6.00 in | 10.5 in |
| 18 in | 3 | 6.00 in | 1 ft 9 in |
| 24 in | 4 | 6.00 in | 2 ft 7.5 in |
| 30 in | 4 | 7.50 in | 2 ft 7.5 in |
| 36 in | 5 | 7.20 in | 3 ft 6 in |
| 42 in | 6 | 7.00 in | 4 ft 4.5 in |
| 48 in | 7 | 6.86 in | 5 ft 3 in |
| 60 in | 8 | 7.50 in | 6 ft 1.5 in * |
* A run of more than about 6 ft is longer than the span trade guides allow for a cut 2×12 stringer, so the stair needs an intermediate support or a different stringer type.
What deck stringers need that indoor ones don't
- More wood under the notch. At least 5 in of uncut wood, compared with the 3½ in often quoted for indoor stairs.
- Limited span. About 6 ft horizontally for cut 2×12 stringers in most sources.
- A solid landing at the bottom, not bare ground.
- A connection built for the load at the top, with a steel connector, never fasteners into end grain.
The deck stairs guide explains each of these, and how many stringers you need for your width.
This tool gives estimates for planning. Deck rules, footing depths and permits vary by location. Confirm the requirements with your local building department before you build.
Frequently asked questions
How many steps do I need for a deck that is 48 inches high?
Divide the height by the riser you want and round up until the riser is 7¾ in or less. For 48 in, seven risers give about 6.86 in each. The deck surface acts as the top step, so you build six treads below it.
Can deck stairs have open risers?
Open risers are allowed, but on a stair more than 30 in above the ground the gap between treads must not let a 4⅜ in sphere pass. With 7 in risers and 1 in treads the gap is about 6 in, so most deck stairs need riser boards or a different detail. The calculator checks this when you select open risers.
What should deck stair stringers rest on?
On a solid landing, such as concrete or pavers, usually at least 36 in long from the nose of the bottom tread. The ground itself shifts and rots wood. Whether the landing needs its own footing, and how deep, depends on your local frost depth and building department.
