Quick Start - Common Projects
Units
Measurements
Floor to floor height
Horizontal space available
Including subfloor and finish
Stair Diagram
Building Code Compliance (IRC 2021)
Rise Requirements
Min: 4"
Max: 7.75"
Run Requirements
Min: 10"
Max: 14"
Comfort Analysis
Based on the 2R + T = 25" comfort rule. Your stairs: 2×7.20 + 10.29 = 24.69"
Materials Estimate
14
Treads
15
Risers
2-3
Stringers
180.0"
Stringer Length
Frequently Asked Questions
What is the ideal stair rise and run?
The ideal residential stair has a rise of 7" (178mm) and run of 11" (280mm). Building codes typically require rise between 4-7.75" and run between 10-14". A comfortable stair follows the rule: 2×Rise + Run = 24-25" (610-635mm).
How do I calculate the number of stairs?
Divide total rise (floor to floor height) by ideal rise (7"). Round to nearest whole number. For example, 108" total rise ÷ 7" = 15.4, so use 15 risers with 7.2" each.
What is a stringer?
A stringer is the diagonal structural member that supports the stairs. It's cut with notches for treads (horizontal) and risers (vertical). You typically need two stringers (one on each side), plus a center stringer for stairs wider than 36".
What are building code requirements for stairs?
IRC 2021 requires: Rise 4-7.75", Run minimum 10", Width minimum 36", Headroom minimum 80", Handrails on one side minimum. All risers and treads must be uniform within 3/8" variation.
What is headroom and how much do I need?
Headroom is the vertical distance from the stair tread nosing to the ceiling above. Building codes require minimum 6'8" (80") headroom at all points. Measure from the nose of each tread to the ceiling directly above.