Stair Calculator — Rise, Run & Riser Height (Code Compliant)
Calculate exact equal riser heights, total run, stringer hypotenuse lengths, and US/UK building code safety compliance.
Project Inputs & Specs
Vertical distance from the bottom finished floor to top finished landing.
Checks if your calculated stair run fits within your hallway or room footprint.
Actual riser height is 7.500" (Passes ≤ 7.75" limit). Tread depth is 10.5" (Passes ≥ 10" limit).
Visual Blueprint & Diagram
Actual Equal Riser Height
14 Risers + 13 Treads across 8.75 ft rise
Purchase 2x12 Framing Lumber at minimum 15 Feet Length
A standard 36-inch wide residential stair requires 3 cut stringers (spaced 16" on center). For 48-inch wide stairs, use 4 stringers.
Stair Rise, Run & Stringer Mathematics
Total floor-to-floor rise is divided by target step heights to determine equal integer risers, from which tread run and stringer hypotenuse are derived:
Risers (N) = Round(Total Rise ÷ Target Riser) | Actual Riser = Total Rise ÷ N | Stringer = √(Total Rise² + Total Run²)Step-by-Step Step Rule:
- 1Measure total vertical rise from finished lower floor to finished upper landing floor.
- 2Input target riser height (standard is 7.5 inches, maximum US code is 7.75 inches).
- 3Specify preferred tread depth (minimum 10.0 inches for residential stairs).
- 4Verify code compliance status and inspect the side-profile blueprint diagram.
How to Calculate Stair Rise, Run & Stringers: Complete Code Manual
Stair building is one of the most strictly inspected phases of residential and commercial carpentry. Inconsistent riser heights are the leading cause of residential trip-and-fall injuries. Modern building codes require every step in a flight to be equal within 3/8 inch, with strict maximum riser heights and minimum tread runs.
US (IRC) vs. UK (Part K) Stair Building Code Comparison
| Specification | US Code (IRC R311.7) | UK Code (Part K Private) |
|---|---|---|
| Maximum Riser Height | 7.75 Inches (197 mm) | 220 mm (8.66 in) |
| Minimum Tread Depth (Going) | 10.0 Inches (254 mm) | 220 mm (8.66 in) |
| Maximum Stair Pitch Angle | ~38° (Recommended 30°-37°) | 42° Max |
| Minimum Headroom Clearance | 6 Feet 8 Inches (2032 mm) | 2.0 Meters (6 ft 6.7 in) |
How to Cut 2x12 Stair Stringers Using a Framing Square
Cut stringers should always be made from clean, knot-free 2x12 dimensional lumber:
- Attach brass stair gauges to your framing square: one at your exact Riser Height on the tongue, and one at your Tread Depth on the body.
- Align the square with the edge of the 2x12 board and trace the step profile, moving down the board for the total number of risers.
- Bottom Riser Drop: Subtract the actual thickness of your tread material (e.g., subtract 1.0 inch for a 5/4 deck board) from the bottom of the stringer so the first step matches all others once treads are installed.
Frequently Asked Questions (FAQ)
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