Gutter slope calculator: how much drop does my gutter need?
1 in of drop
over 40 ft to the downspout · 1 in exact · 1/4 in per 10 ft is 0.025 in per ft, 0.21% · for one downspout, at the SWS minimum
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
1 in of drop
over 40 ft to the downspout · 1 in exact · 1/4 in per 10 ft is 0.025 in per ft, 0.21%
Source: DOE/NREL Standard Work Specifications, detail 2.0201.1 Gutters (2.0201.1c, slope), read October 20, 2026. Read the source
A 40 foot gutter draining to one downspout needs 1 in of drop: the DOE/NREL Standard Work Specifications set a minimum slope of 1/4 inch per 10 feet toward the downspout, which is 0.025 inch per foot.
A worked example
A 57 ft gutter across the back of a house with a downspout at each end, sloped 3/8 inch per 10 feet needs 1 1/8 in of drop. Each half runs 28.5 feet to its downspout, so the high point in the middle sits 1.07 inches above each outlet; marked up to the next 1/16 that is 1 1/8 inches.
How much slope should a gutter have?
At least 1/4 inch for every 10 feet of gutter, toward the downspout, by DOE/NREL Standard Work Specification 2.0201.1c, written so the gutter drains completely. That is 0.025 inch per foot, a 0.21% grade: 1/2 inch over 20 feet and 1 inch over 40. A fall of 1/16 inch per foot is 2.5 times that minimum, and the chart below gives both.
Where does the high point go on a long gutter?
With a downspout at each end, in the middle: each half falls toward its own outlet, so the drop is set over half the length. A 60 ft gutter at the 1/4 inch minimum drops 3/4 inch to each end instead of 1 1/2 inches to one.
What else it is called
Gutter slope is also called gutter pitch or gutter fall, and searched as a gutter slope calculator, gutter pitch calculator or gutter fall calculator. Installers give it in inches per 10 feet or in fractions of an inch per foot; the result shows both, and the grade in percent.
Gutter drop chart
| Run to the downspout | 1/4 in per 10 ft (minimum) | 1/2 in per 10 ft | 1/16 in per ft | 1/8 in per ft |
|---|---|---|---|---|
| 10 ft | 1/4 in | 1/2 in | 5/8 in | 1 1/4 in |
| 20 ft | 1/2 in | 1 in | 1 1/4 in | 2 1/2 in |
| 30 ft | 3/4 in | 1 1/2 in | 1 7/8 in | 3 3/4 in |
| 40 ft | 1 in | 2 in | 2 1/2 in | 5 in |
| 50 ft | 1 1/4 in | 2 1/2 in | 3 1/8 in | 6 1/4 in |
| 60 ft | 1 1/2 in | 3 in | 3 3/4 in | 7 1/2 in |
Drop from the high end to the downspout, rounded up to the 1/16 in. The first column is the minimum slope of DOE/NREL Standard Work Specification 2.0201.1c; with a downspout at each end, read the row for half the gutter length.
Where the numbers come from
- Minimum slope: the Standard Work Specifications for Home Energy Upgrades of the U.S. Department of Energy and NREL, detail 2.0201.1 Gutters, item 2.0201.1c: «Slope all gutters toward the downspout(s) a minimum of 1/4" per 10 feet», with the objective «Ensure complete drainage». Item 2.0201.1a says to size gutters for the area drained and gives no table. Read October 20, 2026. Source
- The rest is geometry: drop = run to the downspout in feet × slope per 10 feet ÷ 10, rounded up to the next 1/16 inch. With a downspout at each end the gutter falls from its middle, so the run is half its length.
This sets the slope of a gutter, not its size: the work specification says to size gutters for the area they drain and gives no figure, so this page does not size them. Measure the drop on the top edge of the gutter, from the high end to the outlet.
By Javier Miralles · Last updated . How this site is made.
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