Stair calculator

Job sheet

Plumb stair job sheet

14 risers, 7.5 in, run 130 in.

  • Risers147.5 in each. IRC residential limit is 7.75 in.
  • Treads1310 in each. IRC minimum is 10 in.
  • Total run130 inNumber of treads times tread depth.
  • Stringer, point to point167.11 inOrder longer stock. This length has no tail past the notch.
  • Concrete if you pour the steps142.19 cu ft · 5.27 cu ydStacked porch volume. Use the concrete sheet for bags and the allowance.
Plumb stair job sheet
14 risers, 7.5 in, run 130 in.

Risers: 14 (7.5 in each. IRC residential limit is 7.75 in.)
Treads: 13 (10 in each. IRC minimum is 10 in.)
Total run: 130 in (Number of treads times tread depth.)
Stringer, point to point: 167.11 in (Order longer stock. This length has no tail past the notch.)
Concrete if you pour the steps: 142.19 cu ft · 5.27 cu yd (Stacked porch volume. Use the concrete sheet for bags and the allowance.)

Stair stringer length

The stringer is the hypotenuse. A 105 inch rise and a 130 inch run (13 treads at 10 inches) is about 167 inches, point to point. The plumb cut at the top and the tail at the bottom eat past those points, so the board has to be longer than 167 inches. Board feet tallies that stock. Joists are a different count.

The count

Risers = total rise ÷ target riser, rounded to a whole number. Actual riser = total rise ÷ that count. Treads = risers − 1. Total run = treads × tread depth. Stringer = the hypotenuse of total rise and total run.

A floor-to-floor rise of 105 inches at a 7.5 inch target is 14 equal risers and 13 treads. Run is 130 inches. The stringer is about 167 inches, point to point. Buy a longer board. The tail and the plumb cut eat length.

If you pour the steps, the width field uses the stacked-porch volume from the concrete calculator. Layout and yards are different jobs. Board feet is where you tally the stringer stock.

Counting a tread for the top riser makes the stair one tread too long. Measure finish floor to finish floor, not subfloor to subfloor.

FAQ

How many stairs do I need?

Count the risers, including the one onto the upper floor. A 105 inch floor-to-floor rise at a 7.5 inch target is 14 stairs. That is 13 treads. The floor at the top is the last tread.

How many risers do I need?

Divide the total rise by the riser you want, then round to a whole number. Every riser, including the one at the top landing, is the same height. A 105 inch rise aimed at 7.5 inches is 14 risers at exactly 7.5 inches.

Why is there one fewer tread than risers?

The top riser lands on the upper floor. That floor is the last tread. Thirteen treads and fourteen risers is the usual count.

What does the code allow?

The 2021 IRC caps a residential riser at 7 3/4 inches and sets a minimum tread depth of 10 inches. The sheet flags those limits. It does not check headroom, handrails, or nosing.

Sources

  1. 2021 IRC, R311.7.5 stair geometry: Residential riser maximum 7 3/4 in and tread minimum 10 in. Confirm the code your town adopted.