How this calculator works
Measure the total length of roof edge (eaves) that needs gutters. The calculator also adds one downspout for roughly every 35 feet of gutter to drain it properly.
Worked example — 120 feet of roofline:
120 linear feet of gutter and about 4 downspouts.
120 linear feet of gutter and about 4 downspouts.
Downspout spacing
One downspout per 30–40 feet of gutter keeps water moving. Long runs or heavy-rain areas benefit from more.
Frequently asked questions
How many downspouts do I need?
About one per 30–40 feet of gutter run.
How do I measure for gutters?
Add up the length of every roof edge (eave) where water needs to drain.