Stair Calculator
Enter the total rise of your stairs and get the number of risers, the riser height, the treads, the stringer and the board to cut it from, with every step shown and every model-code value quoted beside the layout.
Estimates for planning, not professional advice. Read the full notice.
Example: stair layout sheet
Enter the numbers above to see your layout.
Summary
- Risers
- 14 × 7 11/16 in
- Treads
- 13 × 10 in
- Total run
- 130 in
- Stringer (before cut allowance)
- 164 3/16 in
- Framing square
- tongue 7 11/16 in, blade 10 in
- Bottom drop
- 6 11/16 in
- Stock length
- 168 in
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Stair layout sheet
2021 IRC comparison
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Riser height: 7 11/16 in within the 2021 IRC model-code value
The 2021 IRC, section R311.7.5.1, says “The riser height shall be not more than 7 3/4 inches (196 mm).” 7.75 in[1]
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Tread depth: 10 in within the 2021 IRC model-code value
The 2021 IRC, section R311.7.5.2, says “The tread depth shall be not less than 10 inches (254 mm).” 10 in[1]
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Total rise: 108 in within the 2021 IRC model-code value
The 2021 IRC, section R311.7.3, says “A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.” 12 ft[1] 7 in
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Risers: 14 risers
The 2021 IRC, section R311.7.8, says “Handrails shall be provided on not less than one side of each flight of stairs with four or more risers.” 4 risers[1]
-
Tread depth, for the nosing exception: 10 in
The 2021 IRC, section R311.7.5.3, says “A nosing projection is not required where the tread depth is not less than 11 inches (279 mm).” 11 in[1]
-
Open riser gap: 6 11/16 in outside the 2021 IRC model-code value
The 2021 IRC, section R311.7.5.1, says “At open risers, openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below shall not permit the passage of a 4-inch-diameter (102 mm) sphere.” 4 in[1]
Local codes and amendments differ; your building department decides.
Marks from the start
| Mark | Reads | From |
|---|---|---|
| Riser 1 | 7 11/16 in | the floor |
| Riser 2 | 15 7/16 in | the floor |
| Riser 3 | 23 1/8 in | the floor |
| Riser 4 | 30 7/8 in | the floor |
| Riser 5 | 38 9/16 in | the floor |
| Riser 6 | 46 5/16 in | the floor |
| Riser 7 | 54 in | the floor |
| Riser 8 | 61 11/16 in | the floor |
| Riser 9 | 69 7/16 in | the floor |
| Riser 10 | 77 1/8 in | the floor |
| Riser 11 | 84 7/8 in | the floor |
| Riser 12 | 92 9/16 in | the floor |
| Riser 13 | 100 5/16 in | the floor |
| Riser 14 | 108 in (9 ft) | the floor |
| Tread 1 | 10 in | the first riser |
| Tread 2 | 20 in | the first riser |
| Tread 3 | 30 in | the first riser |
| Tread 4 | 40 in | the first riser |
| Tread 5 | 50 in | the first riser |
| Tread 6 | 60 in | the first riser |
| Tread 7 | 70 in | the first riser |
| Tread 8 | 80 in | the first riser |
| Tread 9 | 90 in | the first riser |
| Tread 10 | 100 in | the first riser |
| Tread 11 | 110 in | the first riser |
| Tread 12 | 120 in | the first riser |
| Tread 13 | 130 in | the first riser |
Drawing
A saw-tooth outline of 14 risers and 13 treads. The mark table lists every mark.
Scale 1:24 (1 in = 2 ft) when printed at 100 % (Actual size).
Worked example: a staircase stringer
Show the working
- Risers: divide the total rise by the largest riser, then round up 9 ft ÷ 7.75 in[1] = 14 risers
- Riser height: the total rise divided by the risers 9 ft ÷ 14 risers = 7 11/16 in
- Treads: one fewer than the risers, because the floor above is the top tread 14 risers − 1 = 13 treads
- Total run: the treads times the tread run 13 treads × 10 in = 10 ft 10 in
- Rise below the top riser: the total rise less one riser 9 ft − 7 11/16 in = 8 ft 4 5/16 in
- Stringer before cut allowance: the long side of a right triangle whose short sides are that rise and the total run 8 ft 4 5/16 in = 13 ft 8 3/16 in
- Cut allowance: add what you allow for the end cuts 13 ft 8 3/16 in + 0 in = 13 ft 8 3/16 in
- Stock board: the shortest listed length that is at least as long 13 ft 8 3/16 in = 14 ft
- Bottom drop: the riser less the tread thickness 7 11/16 in − 1 in = 6 11/16 in
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Largest riser you will allow | 7.75 in[1] | |
| Default Prefilled with the 2021 IRC maximum riser height; type a smaller number for more, lower risers. | ||
| Stringer board length | 96 in | |
| Default Common lengths; check your yard. Check your label or supplier. | ||
| Extra length for the cuts on a stringer | 0 in | |
| Default Zero unless you add one. Check your label or supplier. | ||
With a flush mount, the same stair has 14 treads and a total run of 11 ft 8 in.
Layout marks for this example
Where to mark each riser and each tread, measured from the floor and from the first riser
| Mark | Reads |
|---|---|
| Riser 1, from the floor | 7 11/16 in |
| Riser 2, from the floor | 1 ft 3 7/16 in |
| Riser 3, from the floor | 1 ft 11 1/8 in |
| Riser 4, from the floor | 2 ft 6 7/8 in |
| Riser 5, from the floor | 3 ft 2 9/16 in |
| Riser 6, from the floor | 3 ft 10 5/16 in |
| Riser 7, from the floor | 4 ft 6 in |
| Riser 8, from the floor | 5 ft 1 11/16 in |
| Riser 9, from the floor | 5 ft 9 7/16 in |
| Riser 10, from the floor | 6 ft 5 1/8 in |
| Riser 11, from the floor | 7 ft 7/8 in |
| Riser 12, from the floor | 7 ft 8 9/16 in |
| Riser 13, from the floor | 8 ft 4 5/16 in |
| Riser 14, from the floor | 9 ft |
| Tread 1, from the first riser | 10 in |
| Tread 2, from the first riser | 1 ft 8 in |
| Tread 3, from the first riser | 2 ft 6 in |
| Tread 4, from the first riser | 3 ft 4 in |
| Tread 5, from the first riser | 4 ft 2 in |
| Tread 6, from the first riser | 5 ft |
| Tread 7, from the first riser | 5 ft 10 in |
| Tread 8, from the first riser | 6 ft 8 in |
| Tread 9, from the first riser | 7 ft 6 in |
| Tread 10, from the first riser | 8 ft 4 in |
| Tread 11, from the first riser | 9 ft 2 in |
| Tread 12, from the first riser | 10 ft |
| Tread 13, from the first riser | 10 ft 10 in |
Each mark is worked out from the whole rise or run, then written to the nearest sixteenth of an inch. Marks are never added up from the rounded riser height, which would drift.
This example beside the 2021 IRC values
The example's riser, tread, total rise, risers and tread depth beside the quoted model-code values
| Item | This example | Model-code value |
|---|---|---|
| Riser height: within the 2021 IRC value | 7 11/16 in | 7.75 inModel-code (2021 IRC R311.7.5.1) maximum stair riser height; local adopted codes differ. |
| Tread depth: within the 2021 IRC value | 10 in | 10 inModel-code (2021 IRC R311.7.5.2) minimum stair tread depth; local adopted codes differ. |
| Total rise of the flight: within the 2021 IRC value | 9 ft | 12 ft 7 inModel-code (2021 IRC R311.7.3) maximum vertical rise of a flight of stairs; local adopted codes differ. |
| Risers in the flight | 14 risers | 4 risersModel-code (2021 IRC R311.7.8) number of risers in a flight for which the 2021 IRC lists a handrail on one side; local adopted codes differ. |
| Tread depth, for the nosing exception | 10 in | 11 inModel-code (2021 IRC R311.7.5.3) tread depth from which the 2021 IRC text sets no nosing projection; local adopted codes differ. |
Source: 2021 International Residential Code, Chapter 3 Building Planning, International Code Council, 2021 IRC, checked Nov 12, 2026.
A row reads within, outside or at the quoted value. Where the quoted value is a threshold, a row shows the quote alone. These are model-code values; the code your area has adopted may differ.
- The 2021 IRC, section R311.7.5.1, says “The riser height shall be not more than 7 3/4 inches (196 mm).”
- The 2021 IRC, section R311.7.5.2, says “The tread depth shall be not less than 10 inches (254 mm).”
- The 2021 IRC, section R311.7.3, says “A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.”
- The 2021 IRC, section R311.7.8, says “Handrails shall be provided on not less than one side of each flight of stairs with four or more risers.”
- The 2021 IRC, section R311.7.5.3, says “A nosing projection is not required where the tread depth is not less than 11 inches (279 mm).”
In the 2024 IRC these provisions are in Sections R318.7 (stairways) and R321 (guards). The 2024 chapter.
Stairs for common heights
Risers, riser height, treads, total run, stringer and stock board for common total rises, at this example's tread run
| Total rise | Risers | Riser height | Treads | Total run | Stringer | Stock board |
|---|---|---|---|---|---|---|
| 2 ft | 4 risers | 6 in | 3 treads | 2 ft 6 in | 2 ft 11 in | 8 ft |
| 2 ft 6 in | 4 risers | 7 1/2 in | 3 treads | 2 ft 6 in | 3 ft 1 1/2 in | 8 ft |
| 5 ft 2 in: riser within the 2021 IRC value | 8 risers | 7 3/4 in | 7 treads | 5 ft 10 in | 7 ft 4 9/16 in | 8 ft |
| 5 ft 10 in | 10 risers | 7 in | 9 treads | 7 ft 6 in | 9 ft 1 7/8 in | 10 ft |
| 8 ft 1 1/2 in | 13 risers | 7 1/2 in | 12 treads | 10 ft | 12 ft 6 in | 14 ft |
| 9 ft | 14 risers | 7 11/16 in | 13 treads | 10 ft 10 in | 13 ft 8 3/16 in | 14 ft |
| 12 ft | 19 risers | 7 9/16 in | 18 treads | 15 ft | 18 ft 9 7/8 in | 20 ft |
| 12 ft 8 in: total rise outside the 2021 IRC value for one flight | 20 risers | 7 5/8 in | 19 treads | 15 ft 10 in | 19 ft 10 5/8 in | 20 ft |
Every row uses the example's tread run and tread thickness, which are this example's own sizes, and the prefilled largest riser. The stringer is before any cut allowance.
- The 2021 IRC, section R311.7.3, says “A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.”
Questions
How many stairs do I need for my height?
Divide the total rise by the largest riser you will allow, then round the answer up to a whole number of risers. Rounding up keeps every riser at or below that largest size, and the riser height is the total rise divided by that count. With the top tread being the floor above, there is one tread fewer than risers.
How long is a stringer, and which board do I cut it from?
The stringer is the long side of a right triangle whose short sides are the rise below the top riser and the total run. The calculator adds your cut allowance and names the shortest stock length in the fixed list shown in the assumptions that is at least that long. If none of the listed lengths is long enough, it says so.
Why is the bottom step cut shorter?
The first tread sits on top of the stringer's bottom cut and adds its own thickness. The bottom of the stringer is cut shorter by the riser height less the tread thickness, so the first step comes out the same height as the others.
What are the framing square settings?
Set the riser height on the tongue and the tread run on the blade, then mark along both edges. Slide the square along the board and mark every step from the same two points. The calculator shows both settings and the angle of the stringer, which is the slope of the stair.
Can I print the layout?
Yes. The layout sheet lists every mark from the floor and from the first riser, draws the stringer, and prints to scale. A bar on the printout lets you check the scale against a ruler before you mark any board.
Local codes and amendments differ; your building department decides.
Sources (1)
-
2021 International Residential Code, Chapter 3 Building Planning (opens in new tab), International Code Council, 2021 IRC.
Code or government.
“The riser height shall be not more than 7 3/4 inches (196 mm).”
“The tread depth shall be not less than 10 inches (254 mm).”
“A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.”
“Handrails shall be provided on not less than one side of each flight of stairs with four or more risers.”
“A nosing projection is not required where the tread depth is not less than 11 inches (279 mm).”
“At open risers, openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below shall not permit the passage of a 4-inch-diameter (102 mm) sphere.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] International Code Council, 2021 International Residential Code, Chapter 3 Building Planning. Checked November 12, 2026. https://codes.iccsafe.org/content/IRC2021P2/chapter-3-building-planning