Enter the total length of the eaves you will gutter, how many separate runs there are and the height of the eaves. The calculator gives the gutter sections, the number of downspouts and their total length, and the end caps.
Gutter formulas
Sections = gutter length ÷ section length, rounded up Downspouts = gutter length ÷ maximum spacing, rounded up (at least one per run) Downspout length = downspouts × eave height End caps = runs × 2
Worked example: 120 ft of gutter in 3 runs
- Sections of 10 ft: 12.
- Downspouts at up to 40 ft apart: 120 ÷ 40 = 3, at least one per run, so 3.
- Downspout pipe: 3 × 10 ft = 30 ft; end caps: 6.
How many downspouts?
Snohomish County, Washington advises spacing downspouts 20 to 50 ft apart, draining no more than about 700 sq ft of roof to each, and choosing gutters at least 5 in wide. Heavy rainfall, steep roofs and large roof areas need more downspouts or larger gutters, so check local guidance. Corners, miters, hangers and elbows depend on the house and are not counted here.
Questions
How many downspouts for 100 ft of gutter?
At least 3 at 40 ft spacing, or more if the gutter is in several runs.
How many gutter sections do I need?
Divide the total length by the section length; seamless gutters are formed on site in one piece per run.
What size gutter?
Many homes use 5 in gutters; larger roofs and heavy rain may need 6 in.
Sources
- Gutters and Downspouts, Snohomish County, WA.
Used for: Downspouts 20–50 ft apart, about 700 sq ft of roof per downspout, gutters at least 5 in wide.