Basic Stair Dimensions
Floor-to-floor height = 10.00 ft
Stair Calculation Results
Number of Steps
0
steps
Actual Rise
0"
per step
Actual Run
0"
per step
Total Run
0"
0.00 ft
Stringer Length
0'
per stringer
Stair Angle
0°
degrees
Rise + Run
0.0"
Target: 17-18"
2R + G
0.0"
Target: 24-25"
Fraction to Decimal Conversion
| Fraction | Decimal | Fraction | Decimal |
|---|---|---|---|
| 1/16 | 0.0625 | 1/8 | 0.125 |
| 3/16 | 0.1875 | 1/4 | 0.25 |
| 5/16 | 0.3125 | 3/8 | 0.375 |
| 7/16 | 0.4375 | 1/2 | 0.5 |
| 9/16 | 0.5625 | 5/8 | 0.625 |
| 11/16 | 0.6875 | 3/4 | 0.75 |
| 13/16 | 0.8125 | 7/8 | 0.875 |
| 15/16 | 0.9375 | 1 | 1 |
Stair Terminology & Building Codes
Run/Tread
The part you step on. Minimum 10 inches (25.4 cm) per IRC.
Rise/Riser
Height of each step. Maximum 7.75 inches (19.7 cm) per IRC.
Nosing
Protrusion over the riser. 0.75-1.25 inches (1.9-3.2 cm).
Headroom
Minimum 6'8" (80 inches / 203.2 cm) from tread to ceiling.
Stair Width
Minimum 36 inches (91.44 cm) between walls or handrails.
Handrails
Height: 34-38 inches (86-97 cm). Required for stairs with 4+ risers.
Comfort Formulas:
- Rise + Run should be between 17-18 inches
- 2R + G (twice rise + run) should be between 24-25 inches
- Stair angle should ideally be between 30-35 degrees
Stair Calculator: Design Perfect Stairs with Ideal Rise & Run
Building stairs is one of the most precise tasks in construction. Even a small error in the rise or run of individual steps can make a staircase uncomfortable, dangerous, or fail building code inspection. Our Stair Calculator calculates the exact number of stairs, individual rise height, tread depth, and stringer length needed for any project.
Whether you're building interior stairs, exterior deck stairs, or calculating the material needed for a spiral staircase, this tool ensures your stairs meet the standard comfortable ratio of 7:11 (7-inch rise, 11-inch run), which is widely accepted as the most ergonomically comfortable stair proportion.
The calculator helps you comply with International Residential Code (IRC) requirements, which mandate a maximum rise of 7-3/4 inches, minimum run of 10 inches, and minimum headroom of 80 inches.
Key Stair Terminology
Rise: The vertical height of a single step. Building codes typically limit this to a maximum of 7-3/4 inches (IRC).
Run (Tread Depth): The horizontal depth of a single step, measured from front to back. Minimum 10 inches under most building codes.
Stringer: The diagonal board that supports the steps and risers. Most residential stairs use 2 or 3 stringers.
Total Rise: The total vertical height from floor to floor that the staircase must span.
Headroom: The vertical clearance above the stairs. Minimum 80 inches (6 ft 8 in) is required by most codes.
How to Use the Stair Calculator
- Step 1: Enter Total Rise: Measure the total vertical height from the bottom finished floor to the top finished floor in inches.
- Step 2: Enter Preferred Rise: Input your desired rise height per step (recommended: 7 to 7.75 inches).
- Step 3: Enter Preferred Run: Input your desired tread depth per step (recommended: 10 to 11 inches).
- Step 4: Set Stair Width: Enter the width of your staircase to calculate the total number of treads and board feet of material.
- Step 5: Review Results: Get the calculated number of stairs, actual rise height, run depth, total stringer length, and a material list.
Stair Design Formulas
Number of Steps
Steps = Total Rise ÷ Desired Rise HeightAlways round up to the nearest whole number. Then recalculate the actual rise by dividing Total Rise by the number of steps.
Stringer Length
√(Total Rise² + Total Run²)The stringer is the hypotenuse of a right triangle formed by the total rise and total horizontal run. Use the Pythagorean theorem.
Comfortable Stair Ratio
Rise + Run = 17 to 18 inchesA classic building rule: the sum of the rise and run should equal 17-18 inches for comfortable climbing. A 7" rise + 11" run = 18".
Frequently Asked Questions About Stairs
What is a comfortable stair rise?
Most building codes allow up to 7-3/4 inch rise, but 7 inches is generally considered the most comfortable for most adults.
How many stairs for an 8-foot ceiling?
With an 8-foot (96 inch) floor-to-floor height and finished floor thicknesses, you typically need 13-14 steps with a 7-inch rise.
What wood do I need for stair stringers?
Typically 2×12 dimensional lumber (actual 1.5" × 11.25") is used for stringers. You need at least 4-5 inches of solid wood below the cut.
What is the rule of thumb for stair design?
Two rules: Rise + Run = 17-18 inches (comfort formula), and 2 × Rise + Run = 24-25 inches (another common guideline).
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