Stair Calculator | Rise, Run & Stringer Length
Calculate the number of steps, exact riser height, total run, stringer length, and stair angle from total floor-to-floor rise.
Stair Riser, Run & Stringer Length Mathematics
Stair calculator computes the number of steps, exact riser height, total run, stringer length, and stair angle from total floor-to-floor rise.
The total floor-to-floor rise is divided by an ideal riser height (~7.2 in, within standard building-code comfort range) and rounded to a whole number of steps, since a staircase cannot have a fractional step. The stringer (diagonal support board) length is then found with the Pythagorean theorem from the total rise and total run.
- 1Enter the total floor-to-floor rise in inches and the tread depth per step.
- 2View the total number of steps, the exact riser height per step, total horizontal run, stringer length, and stair angle.
A staircase needs to span 108 inches of total rise, using a standard 10.5-inch tread depth.
Frequently Asked Questions (FAQ)
Most building codes and ergonomic guidelines target 7 to 7.75 inches per riser — this calculator uses 7.2 inches as an ideal starting point, then adjusts to a whole number of equal steps.
The stringer is the diagonal structural board (or notched board) that supports the treads and risers — its length is the hypotenuse of the total rise and total run, found via the Pythagorean theorem.
Uneven risers are a leading cause of trip-and-fall accidents on stairs, since people unconsciously expect each step to match the height of the previous one — building codes typically require riser height variance of less than 3/8 inch across a single staircase.
Top Similar Tools (Construction)
Explore more tools in Construction (2+ more calculators available)
Browse our complete directory with category filters, formulas, and verified engines.