Stair calculator
Calculate riser count, actual riser height, tread count, total run, and stringer length for IRC-compliant residential stairs.
Inputs
Stringer mount type
Deck/landing face is top tread — most common for decks
Results
Number of risers
—
risers
Number of treads
—
treads
Total horizontal run
—
Stringer length
—
— buy next standard length up
Stair angle
—
✗ outside comfort range
Comfort formula (R + T)
—
in ⚠ outside 17–18" ideal
IRC code check
—
riser ✗ · tread ✓ · width ✓
⚠ Risers = ⌈Total Rise ÷ Target Riser⌉. Actual riser = Total Rise ÷ Risers (equal distribution per IRC §R311.7.5.1 ⅜" uniformity rule). Stringer = √(Rise² + Run²). IRC R311.7.5: max riser 7¾", min tread 10", min width 36". Comfort formula: Rise + Run = 17–18" (Blondel). Measure finished floor to finished floor — include flooring thickness on both ends. Always verify with your local building department before cutting stringers.