Stair Calculator

Calculate riser height, tread count, total run, stair angle, and code compliance for any staircase.

Total Rise (inches, floor to floor)

Desired Riser Height (in)

Tread Depth (in)

Stair Width (ft)

IRC R311.7 Code Requirements

Max riser height: 7-3/4" (7.75")
Min tread depth: 10"
Min headroom: 6’8" (80")
Min stair width: 36"

Stair Layout

14 risers / 13 treads

Actual riser: 7.71" | Angle: 37.6°

Number of risers	14
Actual riser height	7.71"
Number of treads	13
Total run	130.00" (10.83 ft)
Stair angle	37.6°
Stringer length	14.08 ft
Stair width	3 ft

Stair Profile

info

Sarah Torres:“The 7-10 rule: 7-3/4 max riser, 10 min tread. But the comfortable sweet spot is 7 to 7.5 inch rise with 10 to 11 inch run. Going right to the code max makes a steep stair that your client will complain about.”

Methodology

Number of risers = round(total rise / desired riser height). Actual riser = total rise / number of risers. Treads = risers - 1 (top landing is not a tread). Total run = treads x tread depth. Stair angle = arctan(riser / tread). Stringer length = hypotenuse of total rise and total run. Code references: IRC R311.7 (2021) for residential stairs. Always verify with local building codes — some jurisdictions adopt amendments.

Frequently Asked Questions

How many stairs for a 9-foot ceiling?

A 9-foot ceiling is 108 inches floor to floor (assuming standard floor construction adds about 10-12 inches, making the actual total rise closer to 118-120 inches). At a 7.5-inch riser, that is 16 risers (120 / 7.5). At the code maximum of 7.75 inches, you could use 15 risers (120 / 7.75 = 15.48, round to 15, actual riser = 8.0 inches — which exceeds code). Stick with 16 risers for a comfortable, code-compliant stair.

What is the 7-10 rule for stairs?

The 7-10 rule refers to IRC code maximums: 7-3/4 inch maximum riser height and 10 inch minimum tread depth. These are absolute limits, not targets. A comfortable stair has a 7 to 7.5 inch rise and 10 to 11 inch tread. The classic comfort formula is: 2 x riser + tread = 24 to 25 inches. So a 7-inch riser pairs well with a 10 to 11 inch tread (2(7) + 10 = 24).

How to calculate stair angle?

Stair angle = arctan(riser height / tread depth). For a 7.5-inch riser and 10-inch tread: arctan(7.5/10) = 36.9 degrees. Comfortable residential stairs fall between 30 and 37 degrees. Steeper than 40 degrees feels like a ladder. Shallower than 25 degrees feels like a ramp. Most building codes result in stairs between 30 and 38 degrees when you follow the riser and tread limits.

What is the minimum headroom for stairs?

IRC R311.7.2 requires a minimum 6 feet 8 inches (80 inches) of headroom measured vertically from the stair nosing to any overhead obstruction. This is measured along the entire walking line of the stair, including at the top and bottom landings. Basement stairs often have headroom challenges — if the opening is too small, the header may need to be cut back and reframed.