Stairs Calculator
Risers, treads, total run and stringer length for a straight staircase.
Stairs Calculator
| Number of risers | 13 |
| Actual riser height | 7.38 in |
| Number of treads | 12 |
| Tread depth (from 2R + T rule) | 10.23 in |
| Total run | 122.8 in |
| Total run | 10.23 ft |
| Stringer length (minimum) | 12.99 ft |
A 96 in floor-to-floor rise divides into 13 risers of 7.38 in. That gives 12 treads; the 2R + T = 25 rule sets the tread depth at 10.23 in, a total run of 122.8 in (10.23 ft) and a minimum stringer length of about 13 ft.
Enter the total rise — the finished floor-to-floor height — and the riser height you are aiming for. The calculator picks the whole number of risers that comes closest, then divides the rise evenly so every step is identical, which is what both comfort and code demand.
Tread depth comes from the classic stair formula 2R + T = 25 inches (twice the riser plus the tread is about 25 in; some builders use 25–27 — adjust the target input to your preference). US residential code (IRC) caps riser height at 7¾ inches and requires at least 10 inches of tread depth, so check the result against those limits; the default target of a 7.5-inch riser keeps you inside code.
The formula
Worked example
A 96 in floor-to-floor rise divides into 13 risers of 7.38 in. That gives 12 treads; the 2R + T = 25 rule sets the tread depth at 10.23 in, a total run of 122.8 in (10.23 ft) and a minimum stringer length of about 13 ft.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
Why is there one fewer tread than risers?
The top riser lands you on the upper floor itself, which acts as the final tread — so a staircase always has one less tread board than it has risers.
What are the code limits for stairs?
Under the IRC for residences: maximum riser height 7¾ in, minimum tread depth 10 in (measured nosing to nosing), and risers may not vary by more than 3/8 in within a flight. Local amendments vary, so verify with your building department.
How long a board do I need for the stringer?
The stringer length shown is the straight-line hypotenuse of rise and run — the minimum. Buy the next standard board length up (a 13 ft calculated stringer means a 14 ft board) to allow for the top and bottom cuts.
Category: Construction & Home calculators
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