Enter the total rise your stairs must climb to get the riser count, riser height, tread count, total run and stringer length — code-friendly numbers.
What Is a Stair Calculator?
A stair calculator splits a total rise into equal, code-friendly steps. Building codes typically cap riser height around 7–7.75 inches and require tread depth of at least 10–11 inches — the 7/11 combination is the comfort classic. The method: divide the total rise by the target riser and round UP to whole risers (36 ÷ 7 = 5.14 → 6 risers), then divide the rise evenly (36 ÷ 6 = 6.00 in each). Treads = risers − 1 (the top landing is the last tread), and the stringer is the hypotenuse of rise and run.
How to Use the Stair Calculator
- Enter the total rise in inches (floor to floor).
- Enter your target riser height (7 is standard).
- Enter the tread depth (11 is standard).
- Click “Calculate Stairs” and cut to the actual riser height shown.
Stair Calculator Formula
Risers = ceil(total rise ÷ target riser). Actual riser = total rise ÷ risers. Treads = risers − 1. Run = treads × tread depth. Stringer = √(rise² + run²).
Worked Example
36-inch rise at 7-inch target: 6 risers of 6.00 in, 5 treads, total run 55 in, stringer 65.73 in.
How It Works, In Plain Words
A staircase is one long climb chopped into identical pieces, and the tool does the chopping in three moves. First, it divides the total rise by your target riser and rounds UP: 36 ÷ 7 = 5.14, so 6 risers. Rounding up is the whole game — rounding down to 5 would leave each riser at 7.2 in, above the target and pushing against the code band this page quotes, 7–7.75 in. Second, it shares the rise evenly: 36 ÷ 6 = exactly 6.00 in, and that actual riser height — not the 7 in target — is the number you cut to, because steps must be identical to feel safe underfoot. Third, it lays out the horizontal side: treads are one fewer than risers, because the upper floor serves as the last tread, so 5 treads × 11 in gives a 55 in total run. Finally the stringer length falls out of Pythagoras: √(36² + 55²) = 65.73 in along the slope. Three inputs become a cutting list: how many risers, how tall each one really is, how much floor the flight needs, and how long the sloped board runs.
Real-World Uses
First scenario: a short flight up to a raised deck — exactly the worked example’s territory. The builder enters a 36 in rise, keeps the 7/11 defaults, and gets 6 risers at an actual 6.00 in plus a 65.73 in stringer before cutting anything; the Deck Calculator sits in the Related list because the two jobs so often arrive together. Second: checking whether a planned flight fits the space available. The total run line answers it — 55 in of floor for the example — and if the space is shorter, the tread depth is the honest dial to reconsider, not the riser height. Third: replacing a steep, uncomfortable stair. Entering its total rise with the target left at 7 shows how many risers a comfortable version needs, and why the old one felt wrong: too few risers, each one too tall. In each case the value is the same: the layout is settled on screen, in inches, before any timber is cut.
Benefits of a Stair Calculator
- Rounds to whole risers the safe way (up, never down)
- Actual riser height computed — cut to that number
- Stringer length included for cutting the carriage
- Code-friendly 7/11 defaults
Features of Our Tool
- Instant results in your browser
- No sign-up, no download, 100% free
- Works on mobile, tablet and desktop
- Clear step-by-step explanation below the tool
- Private — your entries never leave your device.
Common Mistakes to Avoid
- Rounding risers down — that makes each riser too tall and the stairs illegal/uncomfortable
- Uneven risers: every riser must be identical, or trips happen
- Forgetting the top landing counts as the last tread (treads = risers − 1)
More Common Mistakes to Avoid
The quietest error is measuring the rise to the wrong surface: the tool wants the floor-to-floor rise, as the How to Use list states, and measuring to an unfinished floor — before the upstairs flooring is down — shifts every riser by the missing thickness. A second trap is treating the target as the answer: 7 in is what you aim at, but the cut follows the actual riser height, 6.00 in in the example; cutting every riser to the target stacks the whole error into the top step. Third, do not read the stringer figure as a plain board length: 65.73 in is the sloped line of the flight, rise and run combined, given so the carriage can be laid out. Finally, keep all three boxes filled — left empty, the tool simply asks for the values again rather than guessing, which is the right behaviour for numbers you are about to cut wood by.
Frequently Asked Questions
How many steps for a 36-inch rise?
6 risers of 6.00 inches each, with 5 treads.
What is a comfortable riser height?
About 7 inches with an 11-inch tread — the classic 7/11 rule. Codes cap risers around 7–7.75 in.
How long is the stringer?
The hypotenuse: √(rise² + run²) = 65.73 in for the example.
How many treads do I need?
One fewer than risers — the upper floor is the last tread.
What is the total run?
Treads × tread depth = 5 × 11 = 55 inches for the example.
Why is the actual riser height different from my target?
Because risers come in whole numbers. The target of 7 in asks for 36 ÷ 7 = 5.14 risers, which cannot be built, so the count rounds up to 6 and the rise is shared evenly: 36 ÷ 6 = 6.00 in each. The actual height lands at or below the target — that is what keeps the flight inside the comfortable band.
Can I use the stringer length to buy timber?
Use it as the layout figure, not a shopping list. The 65.73 in is the sloped hypotenuse of the 36 in rise and 55 in run — the line the stringer follows. A board must cover that line plus the cuts at each end, so treat the figure as the minimum the layout needs and lay the board out before cutting.