Gutter Size Calculator

Find the right gutter size for your roof.

RECOMMENDED
K-style gutter

Usage Tip

5-inch K-style gutters are standard for most homes. Add a downspout every 30–40 ft.

THE MATH
Flow = Area × pitch × rainfall × 0.0105
Where: flow in gallons per hour (GPH)
• 5-inch K-style is standard for most homes
• Add a downspout every 30–40 ft
Scroll to Top

The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.