Stair Calculator
From total rise to a cut stringer.
Type measurements the way you read them off the tape. The drawing, the framing square settings, and the code checks update as you go.
Stair layout
Risers
Closest to your target
Riser height
7 1/8″
7 treads at 10″
Total run
5′ 10″
35.4° stair angle
Stringer
7′ 1 1/4″
Cut from a 8′ 2×12
The dashed line is the edge of the board. Every notch point lands on it, 12 1/4″ apart.
Checks
Riser height. 7 1/8″ is within the 8 1/4″ maximum.
Tread depth. 10″ meets the 9″ minimum.
Nosing. 1″ overhang is in the ¾″ to 1¼″ range required for treads under 11″.
Stringer throat. 5 7/16″ of uncut stock remains behind the notches.
Comfort. 2 × rise + run = 24 3/16″, inside the comfortable 24″ to 25″ range.
One- and two-family dwellings under 780 CMR: 8¼″ maximum riser, 9″ minimum tread. Codes are amended locally and change between editions, so confirm with your building department before you cut.
Laying out the stringer
- 1
Clamp stair gauges on a framing square at 7 1/8″ on the tongue and 10″ on the blade.
- 2
Crown the board up and step off 7 treads. The points along the edge should fall 12 1/4″ apart.
- 3
At the bottom, drop the level cut by the tread thickness so the first riser on the stringer measures 6 1/8″. With the tread on, it finishes at 7 1/8″ like the rest.
- 4
At the top, make the plumb cut and fasten the stringer so its top sits 8 1/8″ below the finished upper floor.
- 5
You need at least 7′ 1 1/4″ of 2×12 per stringer, so buy 8′ stock. Cut one, test the fit, then use it as the pattern for the others.
All dimensions
| Dimension | Fraction | Decimal in |
|---|---|---|
| Risers | 8 | |
| Riser height | 7 1/8″ | 7.094 |
| Treads on stringer | 7 | |
| Tread depth (run) | 10″ | 10.000 |
| Total run | 5′ 10″ | 70.000 |
| Stringer length | 7′ 1 1/4″ | 85.245 |
| Stair angle | 35.4° | |
| First riser cut | 6 1/8″ | 6.094 |
| Stringer drop from upper floor | 8 1/8″ | 8.094 |
| Notch spacing along the edge | 12 1/4″ | 12.261 |
| Throat (uncut stock) | 5 7/16″ | 5.464 |
Reference
What the numbers mean
- Total rise
- The vertical distance from the finished lower floor to the finished upper floor. Measure to finished surfaces, or add the flooring that is still to come. If the ground slopes, measure at the spot where the stair will land.
- Riser height
- Total rise divided by the number of risers. Every riser in a flight should match; codes allow no more than ⅜″ between the tallest and shortest.
- Tread depth (run)
- The horizontal distance from one riser face to the next. The nosing overhang is extra and does not count toward the run.
- Standard and flush mounts
- With a standard mount the stringer hangs one step below the upper floor, so the floor acts as the top tread and the stringer carries one fewer tread than there are risers. With a flush mount the top tread sits on the stringer, level with the floor.
- First riser cut
- Treads raise every step except the floor. Taking the tread thickness off the bottom of the stringer keeps the first step the same height as the others once the treads are on.
- Stringer drop
- How far the top of the cut stringer sits below the finished upper floor. Mark this on the rim or header before you hang the stringer.
- Throat
- The uncut wood left behind the notches, measured square to the board edge. It is what carries the load, so a shallow throat means more stringers, mid-span support, or wider stock.
- Stringer length
- The shortest board the stringer can be cut from, measured tip to tip along the edge. The calculator rounds up to the next stock length.
This calculator is a layout aid, not an engineered design. Stairs also need proper headroom, guards, handrails, landings, and footings. Check your plan with the local building department, and get in touch if you would rather have us build it.