Skip to main content
True Trade Path

Calculator · Free

Stair Calculator

Calculate rise, run, stringer length and headroom to code from total rise.

Stair opening
in

Finished floor to finished floor, not subfloor to subfloor.

in

Nosing to nosing. The IRC minimum is 10 in for a dwelling.

Riser layout

Treads always come out one fewer than risers.

Headroom

Headroom is measured vertically from the tread nosing to the underside of the floor structure above, so it depends on how far back the stairwell is framed.

in

Joist depth plus subfloor and finish floor at the upper level.

in

Rough opening, measured back from the upper floor edge.

Riser height

7-1/4 in× 15 risers

14 treads at 10-1/2 in over a total run of 12 ft 3 in.
TreadsRisers minus one
14
Total run
12 ft 3 in
Stringer lengthDiagonal on the nosing line; add for the top and bottom cuts
15 ft 3 in
Stair angleComfortable stairs land between 30° and 37°
36.6°
HeadroomMinimum 80 in required
87-11/16 in

Riser height 7-1/4 in — within limit

IRC R311.7.5.1 caps the riser at 7-3/4 in. Adding a riser would shorten the step further if you want a gentler climb.

Tread depth 10-1/2 in — within limit

IRC R311.7.5.2 requires at least 10 in of tread depth measured nosing to nosing. Nosing projection does not count toward it.

Headroom 87-11/16 in — clears

A 144 in opening clears the 80 in minimum with 7-11/16 in to spare.

Riser variation 1/4 in — within limit

Laid out at 7-1/4 in per riser, the closing riser works out to 7-1/2 in. The IRC allows no more than 3/8 in between the tallest and shortest riser in a flight, so split the leftover across the flight rather than dumping it on one step.
Riser count options for this total rise
RisersRiser heightTreadsTotal runAngleStatus
147-13/16 in1311 ft 4-1/2 in38.6°Riser too tall
157-1/4 in1412 ft 3 in36.6°Selected
166-13/16 in1513 ft 1-1/2 in34.7°Compliant

Measure the finished floor, then measure it again

Every number here follows from the total rise. If the upper level gets tile and the lower level gets carpet after the stringers are cut, the first and last risers change and the flight can fail the 3/8 in variation rule on its own. Commercial work follows the IBC, which uses a 7 in riser and an 11 in tread — do not carry these dwelling limits onto a commercial job.

What this assumes

  • Checks against IRC R311.7: maximum 7¾ inch riser, minimum 10 inch tread depth for dwellings.
  • Riser heights within a flight must not vary by more than 3/8 inch.
  • Minimum headroom of 6 feet 8 inches is measured vertically from the tread nosing.

Important

Stair geometry is among the most commonly failed residential inspection items and among the most common causes of injury. Commercial stairs follow the IBC, which uses different limits than the IRC values applied here.

Understanding the result

Total rise governs everything

Start from finished floor to finished floor, not subfloor to subfloor. Flooring thickness that differs between levels changes the first or last riser, and an inconsistent riser at the top or bottom of a flight is both a code violation and the single most common trip hazard.

The 3/8 inch rule

The IRC allows no more than 3/8 inch variation between the largest and smallest riser in a flight. People climb stairs from muscle memory after the first two steps, so a single odd riser is what catches a foot.

You may also need

The next decision usually follows directly from this one.

Related trades

Where to go next