Stair Stringer Calculator — Rise, Run, Angle & IRC Code Check

How It Works

1. Measure Total Rise

   Measure the exact vertical distance from the finished floor at the bottom to the finished floor at the top. This is the total rise. Measure at the point where the stairs will be located, not across the room. Floors are rarely perfectly level, so the total rise may vary by location. Measure to the nearest 1/16 inch for accurate riser calculations.

2. Set Target Riser and Tread

   Enter your preferred riser height (typically 7 to 7-3/4 inches for residential) and tread depth (minimum 10 inches per IRC). The calculator finds the number of risers that produces individual riser heights closest to your target while staying within code limits.

3. Review the Layout

   The calculator outputs the number of risers, exact riser height, tread depth, total run (horizontal distance), stringer length (hypotenuse), and stair angle. Verify that the total run fits in the available space. If it does not, adjust the tread depth or consider a landing with a turn.

4. Check Code Compliance

   The calculator flags any values that violate IRC 2021 limits: maximum 7-3/4 inch riser, minimum 10-inch tread, maximum 3/8-inch variation between largest and smallest riser. It also checks headroom clearance (minimum 6 ft 8 in) if you enter the header height.

5. Cut Stringers

   Use the calculated riser height and tread depth to mark your stringer stock with a framing square. The calculator shows the minimum stringer stock length required. Remember to subtract the tread thickness from the bottom riser so all steps feel equal after treads are installed.

Built For

• Carpenters calculating stair layouts for new residential construction before cutting stringers on site
• Deck builders sizing stairs from deck surface to grade with proper riser height and code compliance
• Remodeling contractors planning stair modifications when floor heights change during renovation
• DIY builders designing shop, barn, or loft stairs where the total rise is non-standard
• Building inspectors verifying stair dimensions against IRC residential code requirements
• Concrete contractors calculating form dimensions for poured concrete stairs

Features & Capabilities

IRC 2021 Code Check

Automatically checks riser height (max 7-3/4"), tread depth (min 10"), nosing projection (3/4" to 1-1/4"), and riser variation (max 3/8" between tallest and shortest). Flags non-compliant dimensions with specific code section references.

Optimal Riser Calculation

Finds the number of risers that produces individual riser heights closest to your target. If the total rise is 108 inches and your target is 7.5 inches, the calculator returns 14 risers at 7.714 inches or 15 risers at 7.2 inches and lets you choose.

Stringer Length and Angle

Calculates the hypotenuse length (stringer length) and the stair angle. Shows the minimum stock length needed to cut the stringer. Typical residential stairs run 32-38 degrees. Steeper than 42 degrees feels like a ladder. Shallower than 30 degrees wastes floor space.

Total Run Calculation

Shows the horizontal distance the stairs cover from the face of the top riser to the face of the bottom riser. Compare this to your available floor space. If the run is too long, reduce the tread depth or add a mid-flight landing.

Tread Thickness Adjustment

Enter your tread material thickness and the calculator adjusts the bottom riser cut to compensate. This ensures all risers feel equal after treads are installed, which is the most commonly missed step in stair layout.

PDF Export

Export the stair layout as a branded PDF with all dimensions, code compliance status, and a visual diagram. Take it to the job site for reference while cutting stringers.

Frequently Asked Questions