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Stair Calculator: Risers, Treads and Total Run

Enter your total rise and tread depth to get risers, treads, run and angle, compared with named 2021 IRC figures, with the renumbered 2024 sections noted.

Updated
Reading time3 min
Sources verified

Key takeaways

  • Risers = total rise ÷ 7.75, rounded up, then divide the rise equally among them.
  • Treads are one fewer than risers when the top lands flush.
  • The 2021 and 2024 IRC share the core numbers, but the section numbers changed.

Measure the total rise from finished floor to finished floor, then enter your planned tread depth. The result compares your numbers with figures from the 2021 International Residential Code (IRC). It doesn't tell you a stair meets your local code, so check with your building department.

  • Risers14 at 7.71 inThe fewest risers at or under the 7 3/4 in IRC figure; cut them all the same
  • Treads and total run13 treads, 10 ft 10 inFor a top that lands flush with the upper floor
  • Angle and sloped length37.6° · 14 ft 1 inAlong the nosing line, before stringer cuts
  • Nosing3/4 to 1 1/4 inThe IRC expects a nosing unless treads are at least 11 in
  • HandrailExpected, 34 to 38 inThe IRC calls for one on flights with four or more risers

Nothing you enter leaves your browser. Compares your numbers with the 2021 IRC figures. It doesn't check your local code or the stair's structure.

Show the math with your numbers
  1. Risers: 108 ÷ 7.75 = 13.94, rounded up to 14
  2. Riser height: 108 ÷ 14 = 7.71 in
  3. Run: 13 treads × 10 in = 130 in
What if: tread depth
Tread depthTreads and total run
10 in (yours)13 treads, 10 ft 10 in
10.5 in13 treads, 11 ft 4 1/2 in
11 in13 treads, 11 ft 11 in
12 in13 treads, 13 ft 0 in

How the calculator works

  1. Risers: total rise ÷ 7.75, rounded up
  2. Riser height: total rise ÷ risers
  3. Treads: risers − 1, for a top that lands flush
  4. Total run: treads × tread depth

Worked example

A 108-inch rise with 10-inch treads:

  • 108 ÷ 7.75 = 13.9, so 14 risers at 7.71 inches
  • 13 treads, for a run of 130 inches, or 10 feet 10 inches
  • An angle of about 37.6°

The IRC figures we compare with

Item Figure 2021 IRC 2024 IRC
Maximum riser 7 3/4 in R311.7.5.1 R318.7
Minimum tread 10 in R311.7.5.2 R318.7
Largest difference in a flight 3/8 in R311.7.5 R318.7
Nosing, unless tread is at least 11 in 3/4 to 1 1/4 in R311.7.5.3 R318.7
Headroom 6 ft 8 in R311.7.2 R318.7
Clear width above handrail 36 in R311.7.1 R318.7
Maximum rise, one flight 12 ft 7 in R311.7.3 R318.7
Handrail, at 4 or more risers 34 to 38 in high R311.7.8 R318.7.8, R320.2

We compared the core numbers across editions and found them the same, but your area may use another edition or local changes. There's also an exception for stairs that don't serve a building, porch or deck, which matters for some landscape steps.

What a small change does

Total rise Risers Riser height Run at 10 in treads
30 in 4 7.50 in 30 in
48 in 7 6.86 in 60 in
96 in 13 7.38 in 120 in
108 in 14 7.71 in 130 in
120 in 16 7.50 in 150 in

More risers mean a gentler stair and a longer run, so check you have the floor space first.

Getting the measurement right

  • Measure finished surfaces. Flooring added later changes the top or bottom riser. A mismatch has to stay within the 3/8-inch limit.
  • Check level. The ground under an outdoor stair often slopes, so measure straight down from the top to where the bottom will land, and allow for the slope.
  • Check the landing. The 2021 IRC calls for a landing at the top and bottom of each stairway, at least as wide as the flight and at least 36 inches deep on a straight run. There are exceptions, so check yours.

What this leaves out

This tool doesn't size stringers, check headroom at the opening, or lay out winders or spiral stairs. Structural parts and attachments need your local code, and possibly an engineer. For a deck stair, see guards and balusters.

Frequently asked questions

How many stairs for a 9-foot rise?

A 108-inch rise takes 14 risers at about 7.71 inches, using the 7 3/4-inch figure.

Why is there one fewer tread than riser?

When the top lands flush, the upper floor acts as the last step, so it isn't counted as a tread.

Does this make my stairs code compliant?

No tool can confirm that. It compares your numbers with named figures, while your local building department decides what applies.

Sources

We use primary sources where we can: building codes, federal rules and manufacturer documents. Read our editorial standards.