What is the standard stair riser height?

7 to 7.75 inches in US residential code. 7 to 7.5 inches is most comfortable for daily use.

How wide should stair treads be?

IRC minimum is 10 inches. 11 inches is standard for residential stairs.

What is the steepest legal stair?

In the US: 7.75-inch maximum riser, 10-inch minimum tread. That yields a maximum angle of about 38°.

How do I count steps?

Count risers, not treads. A 14-step stair has 14 risers. The top floor is not a step.

Does the nosing count in the tread depth?

No. Tread depth is measured from the front of one nosing to the front of the next, so nosing overlap is included in the 10-inch minimum.

Staircase Calculator

Total Rise (floor-to-floor)

Vertical distance between finished floors

Target Riser Height

IRC max is 7.75 inches

Tread Depth

IRC min is 10 inches

Formula

numberOfSteps = round(totalRise / targetRiser); actualRiser = totalRise / steps; totalRun = (steps - 1) × tread; angle = atan(rise/run) × 180/π

Pick a target riser height to find how many steps fit your total rise. Divide and round to the nearest whole step. The actual riser height adjusts so all steps are exactly equal. Total run is the number of treads (one less than risers in most stairs) times tread depth. The stair angle is the arctangent of rise over run.

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TL;DR

Enter total rise, target riser height, and tread depth. Get step count, actual riser, total run, and angle.

Enter your floor-to-floor height, a target riser height, and tread depth to get the exact number of steps, actual riser height, total horizontal run, and stair angle. The calculator also checks your design against International Residential Code limits for safety and comfort.

Stair design is one of the most regulated parts of a building. Risers that vary by more than 3/8 inch can cause falls. Riser heights above 7.75 inches violate code and feel uncomfortable underfoot. This calculator works out the exact dimensions that fit your floor-to-floor height while staying within the International Residential Code.

Definition

The computation, step by step

1Measure the total rise from one finished floor to the next.
2Pick a target riser height (7-7.75 inches is the residential sweet spot).
3Pick a tread depth (10-11 inches is typical).
4The calculator divides total rise by target riser and rounds to a whole number.
5It then recomputes the actual riser height so all steps are equal.
6Check the code-compliance message before building.

Solved example

A worked solution

Example: 108-inch rise, target 7.5-inch riser, 11-inch tread

1Steps needed: 108 / 7.5 = 14.4, round to 14
2Actual riser: 108 / 14 = 7.71 inches
3Total run: (14 - 1) × 11 = 143 inches (11 ft 11 in)
4Angle: atan(108 / 143) = 37.1°
5Riser + tread = 7.71 + 11 = 18.71 (above 18 comfort max, consider 7-in riser)

Result: 14 steps at 7.71-inch risers, 143-inch run, 37° angle.

Validity

Edge cases and pitfalls

Measuring rough framing instead of finished floors: The total rise must be finished floor to finished floor. Forgetting to add tile or hardwood thickness can throw the last step off by 0.5 inch or more.
Letting riser heights vary: Code requires all risers within 0.375 inch of each other. People stumble when one step is noticeably different. Adjust the actual riser, not the target.
Forgetting headroom: IRC requires 6 ft 8 in of headroom above the stairs. Steep stairs save floor space but can violate headroom on the floor above.
Confusing number of risers with number of treads: Stairs have one more riser than tread. A 14-riser stair has 13 treads, plus the floor at the top.

Adjacent topics

Related concepts

Term	Definition
Rise	The vertical height of one step. Total rise is the floor-to-floor distance.
Run	The horizontal depth of one tread (not including any overhanging nosing). Total run is the full horizontal stair length.
17-18 inch rule	For comfortable stairs, riser height plus tread depth should sum to 17-18 inches. Outside this range stairs feel steep or shallow.
Nosing	The portion of a tread that extends past the riser below. The IRC requires 0.75 to 1.25 inches of nosing on solid risers.

Applications

Where this calculation appears

New construction planning: Verify stair geometry fits available floor space before framing.
Basement or attic stairs: Design code-compliant stairs for retrofits where space is limited.
Outdoor decks and porches: Calculate steps from grade to deck height for safe outdoor access.
Code review: Verify an existing or proposed stair meets IRC residential code requirements.

Implementation notes

Pro tips

Aim for 7-7.5 inch risers: This range hits the sweet spot for comfort and code. Riser heights above 7.75 inches are illegal in residential US construction.
Use the 17-18 rule first: Pick a riser and tread combination that sums to 17.5 inches. Comfort is built into that ratio.
Plan landings for long stairs: Any stair with more than 12 risers benefits from a landing. It breaks up the climb and is required if vertical rise exceeds 12 feet.
Order tread material with overhang: A 10-inch tread usually has a 1-inch nosing, so the actual board needs to be 11 inches deep. Account for this when buying lumber.

Common questions

Frequently asked questions

Quick reference

Stair Designs for Common Rises

Targeting a 7.5-inch riser and 11-inch tread

Total rise	Steps	Actual riser	Total run	Angle
96 in (8 ft)	13	7.38 in	132 in	36°
108 in (9 ft)typical	14	7.71 in	143 in	37°
117 in	16	7.31 in	165 in	35°
120 in (10 ft)	16	7.50 in	165 in	36°
132 in (11 ft)	18	7.33 in	187 in	35°

For related calculations, try the Room Size Calculator, Concrete Calculator, or Flooring Calculator. Browse all Calculator Online calculators for the full catalog.

Methodology

This calculator uses the standard staircase calculator formula. Results match those from established financial, scientific, and health references.

Reviewed by

Calculator Online Editorial Team. All formulas verified against authoritative sources before publication.

Last updated

2026-05-24