Stair Calculator

Standard residential stair dimensions in the United States typically follow these guidelines:

• Rise (riser height): 7" to 7.75" (178mm to 197mm) - this is the vertical height of each step
• Run (tread depth): 10" to 11" (254mm to 279mm) minimum - the horizontal depth of each step
• Stair width: 36" (914mm) minimum for residential stairs
• Headroom: 6'8" (2032mm) minimum clearance above the stair
• Handrail height: 34" to 38" (864mm to 965mm) above the stair nosing

The International Residential Code (IRC) sets these key requirements for residential stairs:

• Maximum riser height: 7.75" (197mm) - steps cannot be taller than this
• Minimum riser height: 4" (102mm) - steps shouldn't be too shallow
• Minimum tread depth: 10" (254mm) - measured from nosing to nosing
• Uniformity: The largest riser or tread cannot exceed the smallest by more than 3/8" (9.5mm)
• Nosing: 0.75" to 1.25" projection beyond the riser below

Note: Local codes may vary. Always check with your local building department before construction.

To accurately measure for new stairs, follow these steps:

• Total rise: Measure the vertical distance from the finished floor at the bottom to the finished floor at the top. Use a level and tape measure for accuracy.
• Available run: Measure the horizontal space available for the staircase, from where the first step will begin to where the stairs will end at the upper floor.
• Account for flooring: If flooring isn't installed yet, add the thickness of the finished flooring to your measurements.
• Measure multiple times: Take measurements at different points and use the largest measurement to ensure accuracy.
• Consider headroom: Check that you'll have at least 6'8" of clearance above the stair line.

A stringer is the structural backbone of a staircase. Here's what you need to know:

• Definition: A stringer is the diagonal support board that runs along each side of the staircase, holding the treads and risers in place.
• Types: Cut (sawtooth pattern cut into the board) or closed (treads attach to routed grooves)
• Material: Typically made from 2x12 dimensional lumber for residential stairs
• Quantity: Most stairs require at least 2 stringers (one on each side), with wider stairs needing a center stringer
• Calculation: Stringer length is calculated using the Pythagorean theorem: √(total rise² + total run²)

The stringer length shown in this calculator helps you determine the board length needed for your stair stringers.