Gutter Size Calculator
Determine the recommended gutter width based on your roof area and local rainfall intensity.
Covers 5-inch and 6-inch gutters.
Recommended Gutter Size
Gutter sizing uses the roof drainage area and maximum rainfall intensity to determine the water flow the gutter must handle.
Adjusted Roof Area = Roof Footprint × Pitch Factor
Water Flow (gallons/hr) = Adjusted Area × Rainfall Intensity × 0.0104
When using square meters and mm/hr, the calculator converts internally. 1 sq ft = 0.0929 m². 1 inch/hr = 25.4 mm/hr.
Pitch factors:
- Flat to 4/12 pitch: 1.0
- 5/12 to 8/12 pitch: 1.1
- 9/12 to 12/12 pitch: 1.2
Gutter capacity (per 10-foot section):
- 5-inch K-style: handles up to 1,200 sq ft adjusted roof area
- 6-inch K-style: handles up to 2,000 sq ft adjusted roof area
- 5-inch half-round: handles up to 1,000 sq ft adjusted roof area
- 6-inch half-round: handles up to 1,500 sq ft adjusted roof area
Rainfall intensity zones (US):
- Light: 1–2 inches/hr (Pacific Northwest)
- Moderate: 2–4 inches/hr (Midwest, Northeast)
- Heavy: 4–6 inches/hr (Southeast, Gulf Coast)
- Extreme: 6+ inches/hr (tropical zones)