Gutter Slope Calculator Open Calculator
Clean drainage

Rain Gutter Slope Calculator

Plan the slope of a rain gutter so every drop runs to the downspout — find the drop, check an existing slope, or lay out downspouts on a long run.

Rain gutter drop to the downspout
Live

Pick how the gutter drains, set the run and pitch — the drop to build in appears below.

Live preview — the gutter tilts to your drop
level reference drop run HIGH END LOW END →
Gutter (sloped) Water flow Level reference
Enter a run — the drop appears here.
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A rain gutter slope calculator takes the guesswork out of pitching a gutter toward its downspout. The same slope relationship — drop = run × slope — solves four ways here: get the drop from a run and slope, recover the true slope from a measured drop, find the longest run a given drop supports, or split a long gutter into evenly draining sections. Results come in inches, millimetres, grade percent and a 1:X ratio, and the diagram tilts live so the geometry is obvious.

Step by step

Slope a rain gutter right

Interactive — slope a rain gutter step by step
run drop water runs to the outlet

Have a continuous run with no seams? See the seamless gutter slope calculator. To size the downspouts to the rain instead of a rule of thumb, use the gutter flow calculator.

Frequently asked

Questions answered

What slope should a rain gutter have?
Slope a rain gutter at least 1/4 inch for every 10 feet toward the downspout. Many installers use a touch more, up to about 1/16 inch per foot, on long runs or in heavy-rain areas. The point is to keep water moving so it never stands in the channel.
How do I slope rain gutters correctly?
Find the high end and the downspout end, then drop the downspout end by run × slope. For a 30 ft run at 1/4 in per 10 ft that is 0.75 inch. Snap a sloped chalk line from the high mark to the low mark and hang the gutter to it.
Should rain gutters slope one way or two?
Short runs slope one way to a single downspout. Long runs are often crowned high in the middle and sloped both ways to a downspout at each end, which halves the distance water has to travel. The Outlets mode plans both layouts.
Why does my rain gutter overflow even with slope?
Overflow usually means the outlet or downspout can’t carry the flow, the gutter is undersized, or it’s clogged — not always too little slope. Check the flow against roof area and rainfall, and make sure each downspout serves a reasonable length.
Can a rain gutter be perfectly level?
A truly level gutter lets water pond, which breeds debris, corrosion and mosquitoes, and overflows sooner in a storm. Even a slope you can barely see — a fraction of a degree — makes a real difference to drainage.

Need the full gutter slope toolkit?

Switch between drop, slope check, max run and downspout planning on the main calculator — with the same live diagram.

Open the main calculator