Enter the total rise and preferred tread depth — get the number of steps, the exact riser
height, the total run and the stringer length, with automatic code checks.
How stair math works
risers = ceil( total rise ÷ max riser height )
riser = total rise ÷ risers
treads = risers − 1 (top landing acts as the last tread)
total run = treads × tread depth
stringer = √( total rise² + total run² )
The riser count is rounded up so every riser stays under the legal maximum, then the
rise is divided evenly — code requires all risers within ⅜″ of each other, and equal risers
are safer and feel better underfoot.
US residential stair code quick reference (IRC)
| Item | Requirement |
|---|
| Maximum riser height | 7¾″ |
| Minimum tread depth | 10″ |
| Riser variation within flight | ≤ ⅜″ |
| Minimum stair width | 36″ |
| Minimum headroom | 6′ 8″ |
| Handrail height | 34–38″ |
Local amendments vary — always confirm with your building department before cutting.
Frequently asked questions
What is the maximum riser height by code?
The IRC (residential code) allows a maximum riser height of 7¾ inches and a minimum tread depth of 10 inches. Risers within a flight must not vary by more than ⅜ inch. Always confirm with your local building department.
How do I calculate how many steps I need?
Divide the total rise (floor to floor, in inches) by 7.75 and round up — that is your number of risers. Then divide the total rise by that number to get the exact riser height. A 100-inch rise needs 13 risers of about 7.69 inches each.
What is a comfortable riser height?
Around 7 inches with an 11-inch tread is widely considered the most comfortable. A common rule of thumb: riser + tread should total 17–18 inches.
How long a board do I need for the stringer?
The stringer length is the diagonal: √(total rise² + total run²). Buy the next standard lumber length up and expect waste — a stringer with a 100 in rise and 120 in run measures about 156 in (13 ft), so you would buy a 14 or 16 ft 2×12.
How many stringers do stairs need?
Standard 36-inch-wide stairs use three stringers (two outer, one center). Wider stairs add a stringer roughly every 16 inches. Never use fewer than two.