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Stair calculator

Type the floor-to-floor height. You get the riser count and height, the tread depth, the total run, the stringer length and the angle, and every straight-stair rule of the code you pick, with its clause and your number next to the limit.

Units
ft-in
Finished floor to finished floor
Each code's own limits, compared in the code's own unit.
Riser count, tread depth, width, nosing
Empty: the count nearest a comfortable riser for this code
ft-in
Empty: from the code's comfortable step (2R + G)
ft-in
Empty: the rule set's minimum
ft-in
Empty: the rule set's usual nosing

Result

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Worked out in your browser. Nothing you type leaves this page.

How the numbers are worked out

The riser height is the total rise divided by the number of risers, so every riser comes out the same: R = H ÷ n. The page starts with the count closest to a comfortable riser for the code you picked (7 in for the IRC, 175 mm for most of Europe, 170 mm for DIN 18065 and the Turkish rules), never above the code's maximum. Change the count and everything follows.

The tread depth (the going) comes from the step rule 2R + G, the comfortable stride of most stair codes: 25 in in the US, 63 cm in Germany and France. It is kept inside the code's minimum and maximum. Type your own going if the stair has to fit a set run.

The total run is the going times the number of treads, which is one fewer than the risers when the upper floor is the top step. The stringer length shown is the straight line from the bottom of the first riser to the top of the last, the number most people mean; the nosing line beside it runs from the first nosing to the last.

What the code check looks at

Each rule set holds only numbers: the limit, the clause, the edition. No code text is copied. The page checks the riser, the going, the step rule, the angle, the rise of one flight and the number of risers, and the width and nosing when you give them. A stair is shown "within limits" of a rule, never "approved": your building authority decides that.

The German DIN 18065 numbers come from trade summaries, not the standard itself, and say so. The Italian riser and headroom limits are set by each comune. Check the current rules where you build.

Deck stairs

Use the height from the top of the deck boards to the ground or the pad where the stair lands. The same rules apply in most places when the deck serves a house. Under the IRC, a stair from a freestanding deck to the yard can sit outside R311.7; the app says so on the rule sheet.

A worked example

A basement stair with 108 ¾ in from finished floor to finished floor. At a 7 in target that is 15.5 risers, so the page starts with 16 risers of 6 13/16 in. The step rule gives a going of 11 7/16 in, and 15 treads make a total run of 14 ft 3 1/8 in at 30.8°. Set 15 risers and a 10 ½ in going and you get 7 ¼ in risers, a 12 ft 3 in run and 34.6°: steeper and shorter, still within IRC 2021.

Sources

  1. ICC, International Residential Code 2021, R311.7 Stairways
  2. Approved Document K (England), 2013 edition
  3. ISB Bayern, Bautechnik: Treppen (worked example, Lauflänge 383,6 cm)
  4. AWC, DCA 6 Prescriptive Residential Wood Deck Construction Guide
  5. NIST SP 811, Appendix B.9: inch, foot

Results are design aids. Check the current rules with your local building authority before you build.

Checked against the sources on November 2, 2026.

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