Gutters: Length, Falls, and Downspout Spacing
Gutters need a slight fall and enough downspouts to drain. This post covers the length maths and the spacing rule.
What is the Gutter Length Calculator?
Enter the total eaves length and the spacing between downspouts, and the tool gives the gutter length with a 5 percent allowance for joins and the number of downspouts. The allowance is shown separately.
How to use it
- Measure the total eaves length in metres.
- Enter the planned spacing between downspouts.
- Click Calculate Gutters.
Worked example
30 m of eaves with 10 m downspout spacing needs 31.5 m of gutter and 3 downspouts.
How much fall does a gutter need?
A gentle fall toward each downspout, roughly 1 in 600, is a common guide, adjusted to the manufacturer's advice.
Frequently asked questions
Can one downspout serve a long run?
Only for short runs. Long runs need more downspouts or the gutter overflows in heavy rain.
Does gutter size matter?
Yes, larger roofs need larger gutters and downspouts to handle the flow.