Stair Calculator

Building codes typically require: maximum riser height 7.75" (197mm), minimum tread depth 10" (254mm), minimum width 36" (914mm) for residential. The comfort rule states 2×riser + tread should equal 24-25" (61-64cm). Ideal dimensions for comfort: 7" riser with 11" tread or 7.5" riser with 10" tread. All risers and treads must be consistent within 3/8" (10mm).

Divide total rise (floor to floor height) by desired riser height, then round to nearest whole number. For 108" total rise with 7" risers: 108÷7=15.4, round to 15 steps. Actual riser = 108÷15 = 7.2". Number of treads = risers minus 1 (top step is the floor). Verify the actual run fits available space: 14 treads × 10" = 140" needed.

The 17-18 rule states: riser + tread should equal 17-18" (43-46cm) for comfortable stairs. Similar to the 2R+T=24-25 rule. Example: 7" riser + 11" tread = 18" ✓. These formulas ensure natural walking rhythm. Too steep (high riser, short tread) is tiring; too shallow (low riser, long tread) feels awkward. Both rules help design comfortable, code-compliant stairs.

Minimum 2 stringers for stairs up to 36" (91cm) wide. Add a center stringer for wider stairs: 3 stringers for 36-48" (91-122cm), 4 stringers for wider. Stringers should be 2×12 lumber minimum. Pre-cut stringers available at lumber yards for standard rises. For decks and outdoor use, consider steel stringer brackets or pre-made stair systems for durability.

Minimum headroom is 80" (203cm) measured vertically from the nosing of any tread to ceiling above. This clearance must be maintained along entire stair run. For basement stairs and attics, consider the angle of the ceiling or floor above—steeper stairs may reduce headroom. Plan stair opening size before construction to ensure adequate clearance.

DIY materials: $100-500 for basic wood stairs (stringers, treads, risers). Pre-cut stringers: $15-40 each; treads $8-25 each. Deck stairs: $15-25 per step DIY, $50-100 installed. Interior finished stairs: $1,000-5,000+ depending on materials and finish. Spiral stairs: $500-3,000 kit, custom $2,000-10,000+. Factor in railings: $50-200+ per linear foot.