Stair Stringer Calculator

Enter finished-floor total rise, a preferred riser height and tread run in inches. The riser count is rounded to the nearest whole count, so the actual riser can be taller than the preferred value. Review the separately displayed actual height; the preference is not a maximum-height design limit.

Codes vary by location and use, with different limits for commercial and residential stairs. The top and bottom risers depend on flooring thickness, so measure finished floor to finished floor. Stringer material must be sized for the span.

Handrails and guards are required and are separate work.

Number of risers from total rise

Total rise	108
Target riser height	7.5
Tread run	10
Number of risers	14
Stringer length (feet)	14.1
Actual riser height (inches)	7.7

Common error: Cutting the first and last steps the same as the others. The finished floor thickness at the top and bottom changes those two risers unless you adjust the stringer.

Stair Stringer: formula

Steps = round(total rise ÷ target riser); stringer length = √(rise² + ((steps−1) × tread)²)

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Stair Stringer: changing Total rise

Number of risers: assumed Total rise scenarios.
Total rise	Number of risers	Stringer length (feet)	Actual riser height (inches)
86	11	11	7.8
97	13	12.9	7.5
108 (example)	14	14.1	7.7
119	16	16	7.4
130	17	17.2	7.6

Stair Stringer: compare input ranges

Stair Stringer Calculator: Number of risers with each input moved on its own, every other input held at the worked-example value.
Input	Tested from	To	Number of risers: low input	Number of risers: high input	Swing
Total rise	97	119	13	16	3 (21%)
Target riser height	6.8	8.3	16	13	3 (21%)
Tread run	9	11	14	14	0

Stair Stringer: individual input comparisons

Stair Stringer Calculator: change one input at a time; other values remain at the stated example.
Input	Value	Number of risers	Stringer length (feet)	Actual riser height (inches)
Total rise	86	11	11	7.8
	97	13	12.9	7.5
	108	14	14.1	7.7
	119	16	16	7.4
	130	17	17.2	7.6
Target riser height	6	18	16.8	6
	6.8	16	15.4	6.8
	7.5	14	14.1	7.7
	8.3	13	13.5	8.3
	9	12	12.8	9
Tread run	8	14	12.5	7.7
	9	14	13.3	7.7
	10	14	14.1	7.7
	11	14	14.9	7.7
	12	14	15.8	7.7

Number of risers: Total rise against Target riser height

Stair Stringer: Number of risers at combined Total rise and Target riser height settings.
Total rise / Target riser height	6	7.5	9
86	14	11	10
97	16	13	11
108	18	14	12
119	20	16	13
130	22	17	14

Stair Stringer: values and definitions

Worked-example inputs and the results they produce for the Stair Stringer Calculator.
Quantity and definition	Value used
Total rise — Total floor-to-floor rise the stairs must climb, in inches.	108
Target riser height — Preferred height, not a maximum; inspect the calculated actual riser against the adopted requirements.	7.5
Tread run — Depth of each tread, in inches.	10
Number of risers	14
Stringer length (feet)	14.1
Actual riser height (inches)	7.7

Total rise: half and double

Stair Stringer scale comparison; assumed inputs.
Total rise	Number of risers
54	7
108	14
216	29

A staircase divides the total rise into equal steps, and the number of steps sets the riser height. A total rise of 108 inches at a target riser of 7.5 inches gives 14 risers, so each is about 7.7 inches, and there is one fewer tread than risers. With 10 inch treads, the stringer is about 14.1 feet long.

Codes limit the riser and tread sizes for safety, and a step that is uneven trips people, so every riser must match.

Measure the total rise from the finished floor below to the finished floor above, and check your local code for the maximum riser and minimum tread.

Calculate slope on the roof pitch and angle calculator, geometry on the right triangle and Pythagorean pages and lumber on the board feet calculator. The rafter length and deck material pages use similar framing math, and the distance and slope calculator covers the run and rise.

Can the actual riser exceed my preferred height?

Yes. Nearest-integer rounding produces 14 risers at 108 inches total rise, each 7.7143 inches rather than the preferred 7.5. Inspect the actual value against the applicable requirements.

Does the diagonal specify the finished cut?

No. Landings, nosing, finished floor thickness, top and bottom details, headroom, support and structural design remain separate.

Stair Stringer Calculator