Stair Calculator

Calculate stair dimensions for safe, building code compliant construction. Get optimal rise per step, total run, stringer length, number of steps, and materials needed. Automatically checks against IRC building codes and provides warnings for non-compliant designs. Perfect for DIYers and contractors building interior stairs, deck stairs, or any staircase.

Stair Calculator: Calculate stair dimensions for safety and building code compliance. Determines optimal rise, run, stringers, and checks against standard building codes.

Total Rise (Floor to Floor Height)

Measure from finished floor to finished floor

Minimum 10" (25cm), recommended 11" (28cm) including nosing

Minimum 36" (91cm) for residential, 44" (112cm) for commercial

Material Costs (Optional)

How It Works

1. Enter Total Rise

Measure the total vertical distance from the finished floor of the lower level to the finished floor of the upper level. This is the total rise.

2. Set Tread Depth

Enter desired tread depth (the horizontal part you step on). Minimum is 10 inches, but 11 inches is recommended for comfort and code compliance.

3. Specify Stair Width

Enter the width of your stairs. Minimum 36 inches for residential stairs, 44 inches for commercial. Wider is better for safety and moving furniture.

4. Review Results & Compliance

Get number of steps, rise per step, total run, stringer length, materials needed, and building code compliance check with warnings if needed.

Examples

Example 1: Standard Interior Stairs

Total Rise: 9 feet 0 inches (108") Tread Depth: 10 inches Stair Width: 36 inches Results: Number of Steps: 14 treads (15 risers) Rise Per Step: 7.20 inches Total Run: 11 feet 8 inches (140") Stringer Length: 14 feet 6 inches (174") Stair Angle: 33.2° Materials: 3 stringers, 14 treads, 15 risers Status: ✓ Building Code Compliant Standard basement or second floor stairs. Comfortable rise and run ratios.

Example 2: Deck Stairs

Total Rise: 4 feet 6 inches (54") Tread Depth: 11 inches Stair Width: 48 inches Results: Number of Steps: 7 treads (8 risers) Rise Per Step: 6.75 inches Total Run: 6 feet 5 inches (77") Stringer Length: 8 feet 0 inches (96") Stair Angle: 29.7° Materials: 4 stringers, 7 treads, 8 risers Status: ✓ Building Code Compliant Outdoor deck stairs with wider width for easier access. Comfortable shallow rise.

Example 3: Attic Access Stairs

Total Rise: 8 feet 0 inches (96") Tread Depth: 9 inches Stair Width: 30 inches Results: Number of Steps: 12 treads (13 risers) Rise Per Step: 7.38 inches Total Run: 9 feet 0 inches (108") Stringer Length: 11 feet 11 inches (143") Stair Angle: 35.8° Materials: 3 stringers, 12 treads, 13 risers Warnings: • Tread depth (9") is less than minimum 10 inches • Stair width (30") is less than minimum 36 inches • Stair angle (35.8°) is outside ideal 30-35° range Status: ⚠ Review Warnings - May not meet residential building codes. Consider increasing tread depth and stair width.

Frequently Asked Questions

What is the ideal stair rise and run?

The ideal rise (vertical height per step) is 7 to 7.5 inches. Maximum rise allowed by most building codes is 7.75 inches for residential stairs. The ideal run (tread depth) is 10-11 inches minimum. A good rule of thumb: rise + run should equal 17-18 inches, or alternatively, 2×rise + run should equal 24-25 inches. This provides comfortable, safe stairs.

How do I calculate the number of steps needed?

Divide the total rise (floor to floor height) by the ideal rise per step (7.5 inches). Round to the nearest whole number - this is your number of risers. Number of treads (steps you walk on) is one less than risers. Then divide total rise by number of risers to get the actual rise per step. Example: 108" total rise ÷ 7.5" = 14.4, round to 14 risers. 108" ÷ 14 = 7.71" actual rise per step.

How long should stair stringers be?

Stringer length is calculated using the Pythagorean theorem: √(total rise² + total run²). For example, with 108" total rise and 140" total run: √(108² + 140²) = √31,264 = 176.8 inches or about 14 feet 9 inches. Add extra length for attachment to the upper floor. Stringers are typically 2×12 lumber cut to fit the rise and run pattern.

How many stringers do I need?

For stairs up to 36 inches wide, use 3 stringers (one on each side, one in the middle). For stairs 36-60 inches wide, use 4 stringers. For stairs wider than 60 inches, add a stringer every 16 inches for proper support. Stringers must be spaced no more than 18 inches apart. More stringers = stronger, safer stairs with less bounce.

What are common building code violations for stairs?

Common violations: (1) Rise exceeds 7.75 inches, (2) Tread depth less than 10 inches, (3) Stair width less than 36 inches, (4) Inconsistent rise or run (variation >3/8"), (5) Headroom less than 6'8", (6) Missing or incorrect handrails, (7) No landing at top or bottom. Always check local codes before building. Inspections typically required.