Gutter Slope Calculator: Get the Fall Right
A gutter that looks level is a gutter that holds water. This tool works out how much lower the downspout end of your run should sit, in plain inches.
A gutter slope calculator answers the quietest question in the trade: how much fall does this run need? Too little, and water pools in the channel, adding weight and rusting the metal from the inside. Too much, and the gutter line looks crooked against the fascia and water can rush past the downspout outlet in a storm. The right answer is a small, steady fall that the eye can barely see, and it comes from one simple rule.
Most installers pitch a gutter at a quarter inch of fall for every 10 feet of run, toward the downspout. Enter your run length below and the calculator gives the total drop from the high end to the outlet, plus the fall to mark at each 10 foot section.
Please enter a run length between 5 and 300 feet.
Mark the fall with a chalk line snapped between the two ends, and check the first section with a level before the hangers go in. If your existing gutters pool water, the fix is usually a rehang, priced as a repair. Our gutter repair page explains how that works.
How the Gutter Slope Calculator Works
The tool divides your run into 10 foot sections and multiplies by the fall rate you picked. At the standard rate, a 30 foot run drops three quarters of an inch from end to end, and a 40 foot run drops a full inch. That is all the fall a healthy gutter needs. Water in a smooth metal channel moves well on a gentle slope, and a bigger drop buys nothing except a gutter line that visibly tilts against the house. The gentle rate, an eighth of an inch per 10 feet, exists for very long runs where the total standard drop would start to show, or where a downspout at each end splits the run in two.
One honest limit: this tool works out the fall for a straight run to one downspout. Real houses turn corners, and corners change the maths, because each straight section is pitched on its own. Treat the result as the plan for each section, not for the whole roofline at once. When our crews hang a system, they snap a chalk line for every run, set the high end, and let the line, not eyesight, decide the slope.
Why Slope Goes Wrong, and What It Costs You
Slopes rarely start wrong. They drift. A hanger bends under the weight of a clog, ice pries a section down over a winter, or a house settles a fraction and takes the fall with it. The signs are easy to spot once you know them: water standing in the channel a day after rain, overflow at one end during storms while the rest looks fine, and streaks down the siding below the low point. Homeowners ask what kind of trouble poor slope causes, and the answer is a slow chain: standing water rusts seams, the extra weight loosens more hangers, the sag deepens, and a run that needed rehanging ends up needing sections replaced.
The good news is that slope is one of the cheaper gutter problems to put right. Rehanging a sound run at the correct fall is normal repair work, inside the published $100 to $450 per job band. It belongs on the same visit as a clean and a check, which is why our cleaning visits include a slope check. Pair this tool with the gutter size calculator if you are planning a new system: the right size with the wrong slope still overflows, and so does the right slope on a gutter that is too small.
How to Check the Slope on Your Own Gutters
You do not need to climb up with a level to get a first answer. On a dry day, pour a bucket of water slowly into the high end of a run, or run a garden hose at a gentle flow. Watch where the water goes. It should move steadily toward the downspout and drain away within a minute or two. Water that sits still, creeps back toward the middle, or spills over a low spot marks the section that has lost its fall. A second check: the day after rain, look along the channel from a ladder at the end. Standing water you can see is standing proof. Neither test tells you the exact drop in inches, which is what this calculator and a chalk line are for, but together they tell you whether a rehang belongs on your list before the next storm season.
Related guides
Slope is a small number that decides whether water moves or sits. These guides cover hanging runs true and the full install order.
- Hanging gutters with the right slope: pitch math and hanger spacing in practice
- How to install gutters: where slope sits in the full job
Slope questions, answered straight
How much slope do gutters need?
The rule most installers work to is a quarter inch of fall for every 10 feet of run, toward the downspout. Very long runs sometimes use a gentler eighth of an inch per 10 feet, or a high point in the middle with a downspout at each end.
What happens if my gutters are not sloping properly?
Water sits in the channel instead of draining. Standing water adds weight, rusts metal, breeds mosquitoes and spills over the low end in heavy rain. Over time the weight pulls hangers loose, which makes the slope worse. It is a small problem that grows.
Can slope be fixed without replacing the gutters?
Usually, yes. If the metal is sound, a crew can rehang the run at the correct fall with fresh hangers, which sits inside normal repair pricing. Replacement only enters the picture when the gutters themselves are rusted, crushed or pulling away from rotten fascia.
Which end of the run should be high?
The end farthest from the downspout. Water should travel one clear path downhill to the outlet. On a long wall with a downspout at each end, the high point goes in the middle and each half slopes its own way.
Gutters pooling water?
A slope check is part of every cleaning and repair visit. One call gets it measured and priced in writing.
Call +1 (888) 295-0648