- Choose a stair type to load the correct building code limits (IRC residential, IBC commercial, deck, etc.).
- Set the total rise using the slider or type a value. This is the vertical distance from finished lower floor to finished upper floor -- include floor coverings in your measurement.
- Enter the available run -- the horizontal space you have for the staircase.
- Optionally set a desired riser height. Leave blank and the calculator picks the best-fit riser around 7 - 7.5 inches.
- Enter headroom if you want to check clearance above the stair line.
- Review the results: hero dimensions, compliance checks, the side-view diagram, and the material estimate.
Stair Calculator
Stair Type
Primary Dimensions
--
Risers
-- treads
--
Riser Height
--
Tread Depth
--
Total Run
--
Stringer Length
--
Stair Angle
--
Rise + Run (18 Rule)
Building Code Compliance (IRC Residential)
--Staircase Profile (Side View)
Material Estimate
Building Code Reference
Minimum and maximum stair dimensions by code type. The row matching your selected stair type is highlighted.
| Code | Max Riser | Min Tread | Min Headroom | Min Width |
|---|---|---|---|---|
| IRC Residential | 7.75" (196 mm) | 10" (254 mm) | 80" (203 cm) | 36" (91 cm) |
| IBC Commercial | 7" (178 mm) | 11" (279 mm) | 80" (203 cm) | 44" (112 cm) |
| IRC Exterior/Deck | 7.75" (196 mm) | 10" (254 mm) | 80" (203 cm) | 36" (91 cm) |
| Deck (typical) | 7.75" (196 mm) | 10" (254 mm) | 80" (203 cm) | 36" (91 cm) |
How to Use This Calculator
Stair Terminology
- Total Rise: Vertical distance from the finished floor at the bottom to the finished floor at the top of the staircase.
- Total Run: Horizontal distance from the face of the first riser to the face of the last riser.
- Riser: The vertical part of each step. Riser height is measured from the top of one tread to the top of the next.
- Tread: The horizontal part of each step where you place your foot. Tread depth is measured from the face of one riser to the face of the next.
- Stringer: The structural support running diagonally along each side (or center) of the staircase. Its length is the hypotenuse of the rise-and-run triangle.
- Nosing: The front edge of the tread projecting beyond the riser. Typically 0.75 to 1.25 inches.
- Headroom: Vertical clearance measured from the tread nosing to any overhead obstruction. Code minimum is usually 80 inches.
The 18 Rule (Comfort Formula)
For comfortable stairs, the sum of one riser height plus one tread depth should equal 17 to 18 inches. This empirical rule creates stairs with a natural walking rhythm:
- 7" riser + 11" tread = 18" (ideal)
- 7.5" riser + 10.5" tread = 18" (ideal)
- 8" riser + 10" tread = 18" (steep but acceptable)
Why Uniform Risers Matter
All risers in a flight of stairs must be the same height (within 3/8" tolerance). Your brain and muscles memorize the rhythm after the first few steps. If one riser is taller or shorter than the others, it creates a tripping hazard. Building codes strictly enforce riser uniformity for this reason.
Frequently Asked Questions
What is the standard stair rise and run?
For residential stairs, the IRC sets a maximum riser height of 7.75 inches (196 mm) and a minimum tread depth of 10 inches (254 mm). Commercial buildings have stricter requirements: maximum 7-inch risers and minimum 11-inch treads.
How do I calculate the number of steps?
Divide total rise by desired riser height and round to the nearest whole number. Then divide total rise by that number to get your actual riser height. Example: 108" / 7.5" = 14.4, rounded to 15 risers, giving an actual riser of 7.2".
What is the 18 rule for stairs?
The 18 rule states that one riser height plus one tread depth should equal 17 to 18 inches. This balances vertical and horizontal dimensions for a natural walking rhythm. For example: 7" riser + 11" tread = 18".
How do you calculate stringer length?
Stringer length is the hypotenuse of the right triangle formed by total rise and total run. Use the Pythagorean theorem: stringer = sqrt(rise^2 + run^2). For a 108" rise and 130" run, the stringer is about 169" (14 feet).
What is the ideal stair angle?
The ideal angle for residential stairs is 30 to 35 degrees from horizontal. Steeper than 40 degrees becomes uncomfortable and unsafe. Shallower than 25 degrees wastes space and feels awkward.
Can risers be different heights?
No. Building codes require all risers to be uniform with a maximum variation of 3/8" (9.5 mm). Uneven risers are a serious tripping hazard and a leading cause of stair accidents.
How much headroom do I need?
Codes typically require 80 inches (6 feet 8 inches / 203 cm) minimum headroom measured from the tread nosing to any overhead obstruction. This ensures safe passage without ducking.
Do I need a landing?
Most codes require a landing at the top and bottom of stairs with a minimum depth equal to the stair width (at least 36"). For flights with more than 12 feet of vertical rise, an intermediate landing may be required.
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are computed using standard formulas and should be verified for critical applications.
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Stair Calculator FAQ
What is the standard stair rise and run?
For residential stairs, the International Residential Code (IRC) sets a maximum riser height of 7.75 inches (196mm) and a minimum tread depth of 10 inches (254mm). Commercial buildings have stricter requirements: maximum 7-inch risers and minimum 11-inch treads.
How do I calculate the number of steps for stairs?
Divide your total rise (vertical height from floor to floor) by your desired riser height. Round up to the nearest whole number. Then divide the total rise by this number to get your actual riser height. For example, a 108-inch total rise divided by 7.5 inches per riser gives 14.4, which rounds to 15 risers.
What is the 18 rule for stairs?
The 18 rule (also called the stair formula) states that the sum of one riser height plus one tread depth should equal 17 to 18 inches for comfortable stairs. This formula balances the relationship between vertical and horizontal steps to create a natural walking rhythm. For example, 7-inch riser + 11-inch tread = 18 inches.
How do you calculate stringer length?
Stringer length is the hypotenuse of the right triangle formed by total rise and total run. Use the Pythagorean theorem: stringer length = square root of (total rise squared + total run squared). For a staircase with 108-inch rise and 130-inch run, the stringer length is approximately 169 inches or 14 feet.
What is the ideal stair angle?
The ideal stair angle for residential stairs is 30 to 35 degrees from horizontal. This provides a comfortable and safe climbing angle. Stairs steeper than 40 degrees become uncomfortable and potentially unsafe, while stairs shallower than 25 degrees waste space and feel awkward to climb.
Can all risers be different heights?
No. Building codes require all risers in a flight of stairs to be uniform in height, with a maximum variation of 3/8 inch (9.5mm) between the tallest and shortest riser. Uneven risers are a serious tripping hazard and a common cause of stair accidents.