Staircase Calculator - Stairs Rise & Run Calculator
Use this free staircase calculator to determine the number of risers, treads, riser height, total run, and stringer length for your staircase project. Enter your total rise and preferred riser height to get building-code-compliant stair dimensions.
How to Calculate Staircase Dimensions
Building a staircase requires precise calculations to ensure safety, comfort, and compliance with local building codes. The key measurements are the total rise (vertical height from one floor to the next), the riser height (height of each step), and the total run (horizontal distance the staircase covers).
Building Code Requirements for Stairs
The International Residential Code (IRC) sets specific requirements for residential stairs. Risers must be between 4 inches and 7.75 inches in height. Treads must be at least 10 inches deep. The maximum variation between any two risers in the same staircase is 3/8 inch. Handrails are required on at least one side for stairs with four or more risers, and must be between 34 and 38 inches above the stair nosing.
The 7-11 Rule for Stairs
The 7-11 rule is a widely used guideline in stair construction. It states that the ideal stair has a 7-inch riser and an 11-inch tread. This creates a comfortable stepping rhythm that works for most adults. A related formula is that two risers plus one tread should equal approximately 24 to 25 inches. For example, two 7-inch risers plus one 10-inch tread equals 24 inches, which falls within the ideal range.
How to Calculate Stringer Length
The stringer is the diagonal board that supports the treads and risers. To calculate the stringer length, use the Pythagorean theorem: stringer length equals the square root of (total rise squared plus total run squared). For a staircase with a 108-inch rise and 140-inch run, the stringer length would be about 177 inches or approximately 14 feet 9 inches. Always add extra length for cuts at the top and bottom.
Headroom Clearance Requirements
Building codes require a minimum headroom clearance of 6 feet 8 inches (80 inches) measured vertically from the nose of any tread to the ceiling above. This clearance must be maintained along the entire length of the staircase. If your ceiling height limits headroom, you may need to adjust the staircase opening size or consider a different stair configuration such as an L-shaped or U-shaped staircase.
Frequently Asked Questions
What is the ideal riser height for stairs?
The ideal riser height is between 7 and 7.5 inches. This range provides the most comfortable step height for most adults. Building codes set the maximum at 7.75 inches and the minimum at 4 inches. A 7.5-inch riser with a 10-inch tread is one of the most common and comfortable configurations used in residential construction.
What is the 7-11 rule for stairs?
The 7-11 rule states that stairs should have a 7-inch rise and an 11-inch run (tread depth). This ratio creates the most comfortable and safe stair proportion. While modern building codes allow a range of dimensions, the 7-11 proportion remains the gold standard that architects and builders reference. It ensures a natural stride when walking up or down the stairs.
How many stairs do I need for a 9 foot ceiling?
For a 9-foot (108-inch) ceiling, you typically need 15 to 16 risers. However, the total rise is not just the ceiling height. You need to add the depth of the floor framing and subfloor above, which is usually 9 to 12 inches. So the actual floor-to-floor height is approximately 117-120 inches. Divided by a 7.5-inch riser, that gives you 16 risers and 15 treads.
What is the maximum riser height allowed by code?
The International Residential Code (IRC) sets the maximum riser height at 7.75 inches (7-3/4 inches). Some local jurisdictions may have stricter requirements, so always check your local building code before starting construction. The maximum variation between the tallest and shortest riser in the same staircase cannot exceed 3/8 inch.