Gutter Sizing Calculator
Calculate the optimal gutter width, downspout count, and flow capacity based on your roof area, local rainfall intensity, and roof pitch.
Inputs
sq ft
in/hr
/12
Results
Recommended Gutter Width
6 inches
Downspouts Needed9
Estimated Gutter Length164 ft
Required Flow Capacity69.77 GPM
How to Use This Calculator
- Enter Roof Area (sq ft) and Rainfall Intensity (in/hr) from the local 100-year design storm intensity for your region.
- Set Roof Pitch and Number of Corners — steeper pitches and more corners increase flow requirements.
- Review Gutter Width (in) — the calculator recommends the minimum profile (5-inch or 6-inch K-style) for your flow rate.
- Check Downspout Count — the number of downspouts required to prevent overflow during peak storm events.
- Measure Gutter Linear Feet for your eaves to calculate material quantities for replacement or new installation.
- Use Flow Capacity to verify the selected gutter profile can handle the design storm without overtopping.
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