Measure finished floor to finished floor
Total rise is the vertical distance between the two finished walking surfaces. Measuring subfloor-to-subfloor creates riser errors once you add hardwood, tile, or deck boards. Write down the finished floor thickness at both the top and bottom landings before dividing total rise.
The calculator rounds riser count up so the actual step height stays at or below your target. Mark every riser from that single divided measurement instead of rounding each step on the fly.
How do you calculate stair rise, run, and riser count?
Every step in a stair flight must have the exact same vertical riser height so users do not trip. To keep the actual step height at or below your maximum target riser (typically 7.5 in or 7.75 in), divide total floor-to-floor rise by the target riser and round up to the next whole integer:
where:
- Rise_total – Total vertical height from finished lower floor to finished upper floor, measured in inches;
- N_risers – Total number of vertical risers rounded up to a whole step count;
- Run_total – Total horizontal floor space taken by the stairs (Run_total = (N_risers − 1) × Tread). To size the 2×12 diagonal framing lumber, use the stair stringer calculator.
A repeatable layout sequence
- 01
Confirm total rise
Measure between finished levels and account for every finish layer that changes the first or last riser.
- 02
Choose a target, then calculate
Use the target riser only to determine a whole riser count. Divide total rise by that count for the exact step height.
- 03
Separate risers from treads
A standard floor-to-floor flight uses one fewer tread than risers because the upper floor serves as the top step.
- 04
Check the available run
Multiply the number of separate treads by tread depth, then verify the stair fits the space with required landings and clearances.
Worked example: 108 inches of total rise
Start with a 7.5 in target riser. Dividing 108 by 7.5 gives 14.4, which rounds up to 15 risers. Divide 108 by 15 and you get 7.2 in per riser.
A 15-riser floor-to-floor flight has 14 treads. At 10 in per tread, total horizontal run equals 140 in, or 11.67 ft. The step slope equals arctangent(7.2 / 10), or about 35.8 degrees.
Treat these numbers as a layout starting point. Check tread depth, nosing projection, headroom, stair width, handrail height, and local building codes before cutting lumber.
| Layout output | Calculation | Result |
|---|---|---|
| Riser count | 108 ÷ 7.5 = 14.4 (round up) | 15 risers |
| Exact riser height | 108 ÷ 15 | 7.2 in |
| Tread count | 15 risers − 1 | 14 treads |
| Total horizontal run | 14 × 10 in tread | 140 in (11.67 ft) |
| Stair slope angle | arctan(7.2 / 10) | 35.8° |
Common reasons the first or last step changes
- Finish flooring was left out of the initial total-rise measurement.
- The upper landing was counted as an extra tread even though it sits flush with the upper floor.
- The bottom slab, deck, or landing elevation shifted after layout.
- Individual risers were rounded on the tape measure instead of using story-pole divisions.
- Stringer bearing or ledger hanger height shifted the top or bottom step.
Document the geometry before the cut plan
Keep total rise, riser count, exact riser height, tread count, tread depth, total run, and slope angle together on one sketch. Show both finished floor thicknesses on the drawing so you can check the math before making a single saw cut.
OSHA stairway rules apply to workplace and construction stairs rather than residential interiors, yet both standards penalize uneven risers because a 1/4-inch trip hazard at the top or bottom step causes falls.