Stair Calculator
9.00 feet
Standard: 7-7.75"
Minimum: 10"
Building Code Standards
Related Calculators
Understanding Stair Construction
Key Terminology
Rise (Riser Height)
The vertical distance from one step to the next. Standard is 7-7.75 inches.
Run (Tread Depth)
The horizontal distance from front to back of a step. Minimum 10 inches.
Stringer
The diagonal boards that support the steps. Typically cut from 2x12 lumber.
Total Rise
The total vertical height from floor to floor that the stairs must cover.
The 17" Rule
A comfortable staircase follows the rule that the rise plus run should equal approximately 17 inches. For example, a 7" rise with a 10" run = 17". This creates stairs that feel natural to climb.
Formula
Rise + Run = 17" (approximately)
Stringer Length = sqrt(Total Rise² + Total Run²)
Safety Warning
Always check local building codes before construction. Requirements vary by location and stair type (residential, commercial, deck, etc.). Inconsistent rise heights are a leading cause of stair accidents.
Frequently Asked Questions
What is the ideal rise and run for stairs?
Building codes typically require max 7.75" rise and min 10" run. The ideal comfortable stair follows the 'rule of 17': rise + run should equal about 17". Common combinations: 7" rise with 10" run, or 7.5" rise with 10" run.
How do I calculate the number of steps needed?
Divide total rise (floor-to-floor height) by ideal rise height (7-7.5"). For 9 feet (108") total rise: 108 / 7.5 = 14.4, so use 14 or 15 risers. Always verify that calculated rise stays within code limits.
How long should stair stringers be?
Use the Pythagorean theorem: Stringer = sqrt(total rise² + total run²). For 9ft rise and 12ft run: sqrt(81 + 144) = sqrt(225) = 15 feet. Add extra length for landing connections. Standard 2x12 lumber works for most residential stringers.
Why must all risers be the same height?
Inconsistent riser heights are a major cause of stair falls. Building codes require risers to be within 3/8" of each other. Your brain expects consistent steps; even small variations can cause stumbles, especially going down.