Gutter Calculator
Determine gutter size and downspout requirements
Length of each roof edge needing gutters
Distance from eave to ridge
Inches per hour for your area
Drainage Area
—
sq ft
Recommended Gutter Size
—
inches
Downspouts Needed
—
downspouts
Total Gutter Length
—
ft
Estimated Cost
—
USD
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Our gutter calculator determines the right gutter size and downspout count based on roof area and rainfall intensity.
- Measure roof eave length and width to ridge
- Look up maximum rainfall intensity for your area
- Enter specifications
- Add downspouts at corners and low points
AI Insights
Smart analysis for your project
Smart Estimates
Our AI cross-references material costs, regional pricing, and project complexity for more accurate estimates.
Waste Optimization
AI-calculated waste factors based on project type, not flat percentages. Saves 5-15% on material costs.
Best Practices
Recommendations derived from building codes, contractor data, and thousands of completed projects.
Calculation Formula
Drainage area = Roof width x Eave length
Gutter size based on drainage area x rainfall intensity
Downspouts = Gutter length / 30-40 ft spacing
Frequently Asked Questions
What size gutters do I need?
5-inch K-style handles up to 1,200 sq ft drainage area per downspout. 6-inch handles up to 2,400 sq ft.
How far apart should downspouts be?
Every 30-40 feet maximum. For 5-inch gutters, limit each downspout drainage area to 600-800 sq ft.