Find the total rise, from the top of one finished floor to the top of the next. The row gives the number of risers, how tall each one is, how many treads to cut and the stringer length for 10 inch treads. One table is for decks and porches and one is for stairs between floors.
Deck and porch steps
| Floor to floor | Risers | Each riser | Treads | Stringer |
|---|---|---|---|---|
| 14" | 2 | 7" | 1 | 1' 5 3/16" |
| 18" | 3 | 6" | 2 | 2' 2 15/16" |
| 21" | 3 | 7" | 2 | 2' 5" |
| 24" | 4 | 6" | 3 | 3' 2 7/16" |
| 28" | 4 | 7" | 3 | 3' 5 1/16" |
| 30" | 4 | 7 1/2" | 3 | 3' 6 7/16" |
| 36" | 5 | 7 3/16" | 4 | 4' 5 13/16" |
| 42" | 6 | 7" | 5 | 5' 5 5/16" |
| 48" | 7 | 6 7/8" | 6 | 6' 4 7/8" |
Stairs between floors
| Floor to floor | Risers | Each riser | Treads | Stringer |
|---|---|---|---|---|
| 96" | 14 | 6 7/8" | 13 | 13' 5 5/8" |
| 100" | 14 | 7 1/8" | 13 | 13' 8" |
| 102" | 15 | 6 13/16" | 14 | 14' 5 1/4" |
| 104" | 15 | 6 15/16" | 14 | 14' 6 7/16" |
| 105" | 15 | 7" | 14 | 14' 7" |
| 106" | 15 | 7 1/16" | 14 | 14' 7 5/8" |
| 108" | 15 | 7 3/16" | 14 | 14' 8 13/16" |
| 110" | 16 | 6 7/8" | 15 | 15' 6" |
| 112" | 16 | 7" | 15 | 15' 7 3/16" |
| 114" | 16 | 7 1/8" | 15 | 15' 8 7/16" |
| 117" | 17 | 6 7/8" | 16 | 16' 6 1/4" |
| 120" | 17 | 7 1/16" | 16 | 16' 8" |
How this is worked out
The total rise is fixed. It's whatever the floors are. So we pick the whole number of risers that brings each one closest to 7 inches. If two counts are equally close, we take more risers. The steps come out shorter, and they stay inside code longer.
Each riser is the total rise divided by that count. It's carried as an exact fraction, so when you mark the stringer, the last step lands level with the floor.
There's always one tread fewer than risers. The top riser lands on the upper floor, and that floor is the last tread. Counting them the same is how people end up a step short.
The stringer is the straight line from corner to corner over the run, which is the tread count times 10 inches. Buy a board longer than that, since the cuts at the top and bottom take some.
The International Residential Code allows a riser up to 7 3/4 inches and a tread no shallower than 10. Every row here is inside both. Some towns have their own numbers, so check before you cut.
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The chart is on one page in the printable PDF, US Letter size.
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To work out your own sizes, there's a material estimator spreadsheet, and more on the Handyman Calc page.