Stair Calculator
This stair calculator works out the number of risers and treads, exact riser height, tread depth, total run, and stringer length for a straight staircase — with a quick check against common residential code guidelines. Use it as a stairs calculator for a quick layout, a full staircase calculator for a renovation plan, or a simple online stair calculator to double-check a contractor’s numbers.
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Risers = round(Total Rise ÷ Target Riser Height). Once you have a whole number of risers, the actual riser height is Total Rise ÷ Risers, and treads are always one fewer than risers. Enter your total rise below to get every number at once.
Risers = round(Total Rise ÷ Target Riser)How to Use This Stairs Calculator
One measurement drives everything else — get that right and the rest follows.
Measure total rise
Measure the exact floor-to-floor height in feet and inches — from the finished lower floor to the finished upper floor. This is the one number the whole layout depends on.
Set a target riser and tread
Enter the riser height and tread depth you’d like, or tap a preset. The calculator treats these as a starting point, not a fixed answer.
Check the results and code flags
Read the actual riser height, tread count, run, and stringer length, then check the green/red code-guideline rows before you cut anything.
Why Use a Stair Calculator for Riser and Tread Layout
Building a straight staircase starts from one fixed number that can’t be changed: the total floor-to-floor rise. Every riser in the flight has to be exactly the same height, but that total rise almost never divides evenly by a round number like 7.00 inches. A staircase calculator handles that rounding automatically — picking a whole number of risers, then spreading the total rise evenly across them, so every step ends up identical instead of one odd-height riser at the top or bottom.
Because a stair also has a horizontal footprint, this stair calculator solves for total run (tread depth × number of treads) and the stringer length — the diagonal support board the treads and risers attach to — at the same time. It then checks the result against widely cited residential guidelines for maximum riser height, minimum tread depth, and the classic “comfort formula” that balances the two against each other.
DIYers framing a deck stair, contractors roughing out a quick layout, and homeowners planning a renovation all benefit from seeing riser count, tread count, run, and stringer length together instead of computing each by hand.
How This Stair Calculator Goes From Total Rise to a Finished Stair
Every stair starts from one fixed number — the total floor-to-floor height — and works backward to find a riser height that divides evenly into it.
Number of risers
Risers = round(Total Rise ÷ Target Riser Height), then the actual riser height is recalculated as Total Rise ÷ Risers so every step ends up exactly equal.
Number of treads
A straight stair always has one fewer tread than risers, since the top step is the upper floor itself: Treads = Risers − 1.
Total run & stringer length
Total run is Treads × Tread Depth. Stringer length is the diagonal: √(Total Rise² + Total Run²), the board length needed before notching.
The comfort formulas
Two common rules of thumb for a comfortable stair: 2 × Riser + Tread ≈ 24–25", or Riser + Tread ≈ 17–18". Both balance a shorter riser against a deeper tread, or vice versa.
Common Riser & Tread Configurations at a Glance
The three presets built into the calculator above, side by side, with what each is best suited for.
| Configuration | Riser | Tread | Comfort formula | Best for |
|---|---|---|---|---|
| Standard interior | 7.00″ | 10″ | 24.0″ | Most interior residential stairs |
| Max-code / space-saving | 7.75″ | 10″ | 25.5″ | Tight basements, limited floor space |
| Comfortable / exterior | 6.00″ | 12″ | 24.0″ | Deck stairs, exterior entries, accessibility |
Stair Calculator: Worked Examples
Three common situations worked end-to-end using the same rise-to-run formulas as the calculator above.
Standard interior stair, 9 ft floor-to-floor
A house has a 9’0″ floor-to-floor rise. Using a 7″ target riser and 10″ tread, how many steps result?
Given inputs
- Total rise: 108 in (9’0″)
- Target riser: 7 in
- Tread depth: 10 in
Computed outputs
- Risers: round(108 ÷ 7) = 15
- Actual riser height: 108 ÷ 15 = 7.20″
- Treads: 14 · Total run: 140″ (11’8″)
- Stringer: √(108² + 140²) ≈ 176.8″ (14’8.8″)
Space-saving stair at max code riser height
A basement stair has an 8’6″ rise and limited floor space. Using the max-code preset (7.75″ riser, 10″ tread), what’s the footprint?
Given inputs
- Total rise: 102 in (8’6″)
- Target riser: 7.75 in
- Tread depth: 10 in
Computed outputs
- Risers: round(102 ÷ 7.75) = 13
- Actual riser height: 102 ÷ 13 = 7.85″
- Comfort check: flagged — 7.85″ exceeds the common 7¾” max
- Treads: 12 · Total run: 120″ (10’0″)
Comfortable exterior deck stair
A deck stair has a 3’6″ rise down to grade. Using the comfortable/exterior preset (6″ riser, 12″ tread), what’s the layout?
Given inputs
- Total rise: 42 in (3’6″)
- Target riser: 6 in
- Tread depth: 12 in
Computed outputs
- Risers: round(42 ÷ 6) = 7
- Actual riser height: 42 ÷ 7 = 6.00″ (exact)
- Treads: 6 · Total run: 72″ (6’0″)
- Comfort check: passes — 2×6 + 12 = 24″ fits the 24–25″ range
Stair Calculator Mistakes to Avoid
Assuming your target riser height is the final one
The target riser is a starting point, not the result. Because the total rise rarely divides evenly, the actual riser height the calculator returns is almost always a fraction of an inch different — and that final number is what needs to be built to, not the original target.
Forgetting nosing in the tread depth
Many codes allow the tread’s “run” measurement to include a small nosing overhang beyond the riser below it. Confusing total tread board depth with the code-measured run can throw off both the total-run figure and a code comfort check.
Ignoring headroom clearance
This calculator solves rise, run, and stringer length — it doesn’t check the vertical clearance above each tread. A stair that passes every riser and tread check can still fail on headroom if the floor or ceiling above cuts it too close.
Using inconsistent units for rise
Entering rise partly in feet and partly as a decimal inch that doesn’t match (like “9 ft, 6 in” typed as 9.5 inches instead of 6 inches) silently shrinks the total rise and produces a stair with the wrong number of risers.
Skipping the professional check on exit stairs
Interior residential stairs, exterior stairs, and exit-access stairs in commercial buildings often follow different code sections with different limits. A layout that’s fine for a basement stair may not meet requirements for an egress stair — verify against the applicable code, not just general residential rules.