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
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.