IRC-safe riser height, tread depth, and stringer length from a total rise.
Floor to finished floor above
IRC allows 7 to 7.75 in
Risers
Actual riser: 7.714 in
14
Treads
13
Total run
11.92 ft
143.00 in
Stringer length
Includes 12 in top overrun
191.20 in
Stair width
36.0 in
Stair math starts with total rise — the exact floor-to-floor height in inches, including finish flooring both above and below. Divide by your preferred riser (7.5 in is the sweet spot), round to the nearest whole number, then divide total rise by that count to get the actual riser.
Tread count is always risers minus one because the top tread is the floor you’re arriving on. Stringer length is the hypotenuse of rise × run plus about a foot of overrun for the top plate and landing attachment — always cut stringer stock long and trim.
risers = round(total_rise ÷ preferred_riser)
actual_riser = total_rise ÷ risers
treads = risers − 1
total_run = treads × tread_depth
stringer = √(rise² + run²) + 12 in