Stair Stringer Calculator: Rise, Run and Length

Enter the floor-to-floor rise, a target riser height and a tread depth.

Last reviewed 29 Oct 2026

Your measurements

Enter the total rise and the step sizes you would like. Everything updates as you type.

The flight

Total rise, floor to floor

From the finished lower floor to the finished upper floor, measured at the stairs.

Target riser height

What you would like. The calculator rounds to a whole number of risers, then gives the exact height.

Tread depth

The horizontal depth of each step along the stringer, not counting the overhang.

The stringer board

Stringer board width

The real width, not the nominal one. A 2x12 is about 11.25 in.

Tread thickness

Used to shorten the first riser cut. Two 2x boards or one 5/4 deck board are typical; measure yours.

Risers14

Number of risers

14risers

= 13 treads, the upper floor is the top step

Each riser is 7.5 in. The stringer angle is 36.87 degrees and 5.25 in of wood is left under the notches.

Riser height: 7.5 in; = 191 mm; Target was 7.25 in
Total run: 130 in; = 3302 mm; 13 × 10 in
Board to buy: 14 ft; Layout line 13.93 ft (167.11 in)
First riser cut: 6 in; = 152 mm; Riser less 1.5 in tread

Check before you cut

The 14 ft board is only 0.9 in longer than the layout line. The end cuts need some extra, so check the layout on the board or buy the next length up.

Layout marks

Height of each step and its distance from the first riser, in tape-measure fractions. Step 1 is the bottom step; the last step is the upper floor.

Step	Height of the step	Distance from the first riser
1	7 1/2"	0"
2	15"	10"
3	22 1/2"	20"
4	30"	30"
5	37 1/2"	40"
6	45"	50"
7	52 1/2"	60"
8	60"	70"
9	67 1/2"	80"
10	75"	90"
11	82 1/2"	100"
12	90"	110"
13	97 1/2"	120"
14	105"	130"

How this was calculated

Risers, run, stringer length, angle and throat, with your numbers.

Step 1: Number of risers
total rise ÷ target riser, rounded to a whole number
= 105 ÷ 7.25 = 14.48
= 14 risers
A flight has a whole number of risers, so the target riser height is only a starting point. The top step is the upper floor, so it counts as a riser but has no tread.
Step 2: Exact riser height
total rise ÷ risers
= 105 ÷ 14
= 7.5 in (7 1/2")
Every riser is this height. Code usually limits how much risers may differ from each other, so cut them all the same.
Step 3: Treads and total run
treads = risers − 1, total run = treads × tread depth
= 14 − 1 = 13, 13 × 10
= 13 treads, 130 in of run
The upper floor is the last step, so there is one less tread than risers. The run is how far the stairs reach along the floor.
Step 4: Stringer length
√(total rise² + total run²)
= √(105² + 130²)
= 167.11 in (13.93 ft)
This is the layout line along the stringer. Buy the next standard length, 14 ft. The end cuts need a little extra, so check the layout on the board before you cut.
Step 5: Stringer angle
atan(riser ÷ tread)
= atan(7.5 ÷ 10)
= 36.87 degrees
The angle of the stairs from the floor. A framing square set to the riser and tread gives you this angle without measuring it.
Step 6: Wood left under the notches (throat)
board width − (riser × tread) ÷ √(riser² + tread²)
= 11.25 − (7.5 × 10) ÷ √(7.5² + 10²)
= 5.25 in
The shortest distance from the inside corner of a notch to the far edge of the board. This is the wood that carries the load, so a thin throat is a weak stringer.
Step 7: First riser cut
riser − tread thickness
= 7.5 − 1.5
= 6 in (6")
The bottom of the stringer is cut shorter by the thickness of a tread, so the first step is the same height as the others once its tread is on.
Step 8: Comfort check
2 × riser + tread, and riser + tread
= 2 × 7.5 + 10, 7.5 + 10
= 25 in and 17.5 in
Rules of thumb: stairs that feel comfortable usually have 2 × riser + tread between 24 and 25 in, and riser + tread between 17 and 18 in. They are guides, not code.

In short

A 105 in total rise at a 7.25 in target riser gives 14 risers of 7.5 in and 13 treads of 10 in. The run is 130 in and the stringer layout line is 167.11 in (13.93 ft), so buy a 14 ft board.

You get a whole number of risers, the exact riser height, the total run, the stringer board to buy, the angle and the marks to lay out with a tape.

Risers and run for common rises

Worked with a 7.25 in target riser, a 10 in tread and a 11.25 in wide stringer board. The rises are examples; measure your own.

Total rise	Risers	Riser height	Total run	Stringer line	Board
96" (8 ft)	13	7.385"	120"	153.67"	14 ft
105" (8.75 ft)	14	7.5"	130"	167.11"	14 ft
108" (9 ft)	15	7.2"	140"	176.82"	16 ft
111" (9.25 ft)	15	7.4"	140"	178.66"	16 ft
120" (10 ft)	17	7.059"	160"	200"	20 ft

Typical values worked out with the formulas on this page, not a code table. Your local code decides the limits.

Worked example: 105 in rise, 10 in tread, 11.25 in board

Target riser 7.25 in, 1.5 in treads.

Step 1: Number of risers
total rise ÷ target riser, rounded to a whole number
= 105 ÷ 7.25 = 14.48
= 14 risers
A flight has a whole number of risers, so the target riser height is only a starting point. The top step is the upper floor, so it counts as a riser but has no tread.
Step 2: Exact riser height
total rise ÷ risers
= 105 ÷ 14
= 7.5 in (7 1/2")
Every riser is this height. Code usually limits how much risers may differ from each other, so cut them all the same.
Step 3: Treads and total run
treads = risers − 1, total run = treads × tread depth
= 14 − 1 = 13, 13 × 10
= 13 treads, 130 in of run
The upper floor is the last step, so there is one less tread than risers. The run is how far the stairs reach along the floor.
Step 4: Stringer length
√(total rise² + total run²)
= √(105² + 130²)
= 167.11 in (13.93 ft)
This is the layout line along the stringer. Buy the next standard length, 14 ft. The end cuts need a little extra, so check the layout on the board before you cut.
Step 5: Stringer angle
atan(riser ÷ tread)
= atan(7.5 ÷ 10)
= 36.87 degrees
The angle of the stairs from the floor. A framing square set to the riser and tread gives you this angle without measuring it.
Step 6: Wood left under the notches (throat)
board width − (riser × tread) ÷ √(riser² + tread²)
= 11.25 − (7.5 × 10) ÷ √(7.5² + 10²)
= 5.25 in
The shortest distance from the inside corner of a notch to the far edge of the board. This is the wood that carries the load, so a thin throat is a weak stringer.
Step 7: First riser cut
riser − tread thickness
= 7.5 − 1.5
= 6 in (6")
The bottom of the stringer is cut shorter by the thickness of a tread, so the first step is the same height as the others once its tread is on.
Step 8: Comfort check
2 × riser + tread, and riser + tread
= 2 × 7.5 + 10, 7.5 + 10
= 25 in and 17.5 in
Rules of thumb: stairs that feel comfortable usually have 2 × riser + tread between 24 and 25 in, and riser + tread between 17 and 18 in. They are guides, not code.

Before you cut

Measure the total rise from the finished lower floor to the finished upper floor. If flooring will be added at the top or bottom, include its thickness first.
The riser limit of 7.75 inches and tread minimum of 10 inches are typical US residential limits. Your local code decides, and it also covers handrails, headroom, landings and the maximum rise of one flight.
The stringer length is the layout line along the board. The plumb and level end cuts need a little extra wood, so if the line is close to a standard length, take the next one up.
Lay out one stringer, cut it, test it in place, and use it as the pattern for the others. Use enough stringers for the width and the tread material; check what your local code asks for.

Stair stringers: common questions

Risers, treads, limits and the first cut.

How do you work out the number of stairs from the total rise?

Divide the total rise by the riser height you want and round to a whole number. A 105 inch rise divided by 7.25 inches is 14.48, so use 14 risers. Then divide the rise by 14 to get the exact riser height, 7.5 inches. The upper floor is the top step, so 14 risers need only 13 treads.

What riser height and tread depth are allowed?

Typical US residential limits are a riser of 7.75 inches or less and a tread of at least 10 inches (IRC R311.7). Your local code decides, and it may differ. The calculator flags a riser or tread outside those typical limits but does not block it.

Why is the first riser cut shorter?

The bottom of the stringer rests on the floor, and the first tread sits on top of the first notch. If the first riser were cut full height, the first step would end up one tread thickness taller than the rest. Cutting it shorter by the tread thickness makes every step the same height once the treads are on.

Is a 2x12 wide enough for a stringer?

Usually, for a normal flight, but check the wood left under the notches (the throat). The calculator shows it, and flags anything under 3.5 inches as thin. With a 7.5 inch riser and a 10 inch tread a real 11.25 inch 2x12 leaves 5.25 inches. Steeper or deeper steps leave less.