Gutters are sized for the roof area that drains into them and the rainfall intensity where you work. Placing the outlets well matters as much as the gutter size.
Common sizes
Residential gutters are usually 5" K-style, with 6" for large or steep roofs and heavy-rain areas. Downspouts are typically 2×3" or 3×4".
Outlets
Put an outlet roughly every 30–40 ft of gutter, and close to valleys, which deliver a lot of water to one spot. A centre outlet with the gutter falling both ways doubles the capacity of a run.
Fall
About ¼" per 10 ft is typical, enough to drain without looking crooked.
The full fitting list
- Gutter lengths and connectors
- Hangers every 24"
- End caps, corners and outlets
- Downspouts, elbows and straps
- Leaf guards, if wanted
This guide is general information for estimating. It is not engineering, legal or tax advice. Check local codes and your inspector for your project.