Stair Calculator

Formula

risers = round(totalRise / desiredRiser)actualRiser = totalRise / riserstreads = risers − 1totalRun = treads × treadDepthstringerLength = √(totalRise² + totalRun²)2R+T = 2 × actualRiser + treadDepth (comfort: 24-25")

Parameters

Total Rise

Floor-to-floor height (default: 108" / 9 ft).

Desired Riser

Target riser height (default: 7.5").

Tread Depth

Tread depth (default: 10").

Stair Width

Width of staircase (default: 36").

Results

Risers

Number of riser steps.

Actual Riser

Exact riser height after rounding.

Treads

Number of treads (risers − 1).

Total Run

Horizontal distance of staircase.

Stringer Length

Diagonal length of stringer board.

Angle

Stair angle in degrees.

2R+T Comfort

Should be 24-25" per IRC.

Example

risers = round(108 / 7.5) = 14actualRiser = 108 / 14 = 7.7"treads = 13, totalRun = 130"stringer = √(108² + 130²) = 169.0"2R+T = 2(7.7) + 10 = 25.4" ✓

Common Use Cases

• Residential staircase design
• Deck stairs and outdoor steps
• Code compliance verification
• Stringer cutting layout

Notes

• IRC residential: max riser 7.75", min tread 10".
• IBC commercial: max riser 7", min tread 11".
• 2R+T comfort rule: aim for 24-25" for comfortable stairs.
• Minimum stair width: 36" (residential IRC) measured above the handrail. Hallway-clearance requirements often dictate a wider stairwell opening.
• Headroom minimum: 6'8" (80") measured plumb above the nosing line — critical for basement stairs cut into joists.

Frequently Asked Questions