Stair Calculator
Calculate stair rise, run, stringer length, angle, and more with our free stair calculator. Automatic or manual mode with imperial/metric units.
Calculation Results
How to Calculate Stairs
Calculating stairs requires precise measurements to ensure safety and compliance with building codes. Our stair calculator simplifies this process by automatically determining the optimal number of steps, riser height, tread depth, and stringer length based on your total rise measurement.
Stair Calculation Formulas
The fundamental formulas used in stair calculations are:
- Number of Risers = Total Rise ÷ Riser Height
- Total Run = (Number of Treads) × Tread Depth
- Stringer Length = √(Total Rise² + Total Run²)
- Stair Angle = arctan(Total Rise ÷ Total Run)
Building Code Requirements
Most building codes, including the US International Residential Code (IRC), specify these limits:
- Maximum riser height: 7.75 inches (196 mm)
- Minimum tread depth: 10 inches (254 mm)
- Minimum headroom: 6 feet 8 inches (2032 mm)
- Maximum variation between risers: 3/8 inch (9.5 mm)
Recommended code limits: riser ≤ 7.75 in (US IRC), headroom ≥ 6’8″. Always consult your local building department for specific requirements. ICC/IRC Reference
Stair Calculator Modes
Our calculator offers two modes:
- Automatic Mode: Enter only the total rise, and the calculator will recommend optimal riser height and calculate all other dimensions.
- Manual Mode: Specify total rise, total run, number of steps, and other parameters for custom calculations.
Stair Stringer Calculator
The stair stringer is the structural component that supports the treads and risers. Calculating the correct stringer length is crucial for proper stair construction. Our stringer calculator uses the Pythagorean theorem to determine the exact length based on total rise and total run.
Deck Stair Calculator
When building deck stairs, consider additional factors like material thickness, weather resistance, and local building codes. Our deck stair calculator accounts for these variables to ensure your outdoor stairs are safe and durable.
Frequently Asked Questions
The ideal riser height is typically between 7 and 7.75 inches (178-197 mm). Most building codes set the maximum at 7.75 inches. Our calculator automatically recommends optimal riser heights based on your total rise measurement.
To calculate the number of steps, divide the total rise by your desired riser height. Round up to the nearest whole number, then recalculate the actual riser height by dividing the total rise by the number of steps.
The stringer length is calculated using the Pythagorean theorem: √(Total Rise² + Total Run²). Our calculator automatically computes this based on your inputs.
Most building codes require a minimum of 6 feet 8 inches (2032 mm) of headroom above the stair nosings. Our calculator includes an optional headroom calculation to ensure compliance.
Rise refers to the vertical height of each step, while run refers to the horizontal depth of each tread. Total rise is the overall vertical height the stairs must cover, and total run is the horizontal distance the stairs will occupy.
Yes, our stair calculator works for both interior and exterior stairs, including deck stairs. Just ensure you select appropriate materials and consider weather factors for outdoor applications.