Gutter slope calculator

How much a gutter run should drop toward the downspout, end to end.

Measure your eave runs and confirm capacity, spacing and coverage against the exact product you buy. Allow extra for corners, waste and slope (~5–10%). Sizes, capacities, spacings and panel lengths vary by product and brand — read the label and the manufacturer’s data.

Calculator

ft
in
0.25–0.50 in per 10 ft
Result
Total drop over the run1.00 in
Run length40 ft
Slope used0.25 in per 10 ft
Recommended slope range0.25–0.50 in / 10 ft

A 40-ft run at 0.25 in per 10 ft drops 1.00 inches end to end. Slope the gutter toward the downspout about ¼–½ inch per 10 feet; a mid-run high point can drain both ways to two downspouts.

A gutter that sits dead level holds standing water — it breeds mosquitoes, corrodes and overflows. It needs a gentle, deliberate slope toward the downspout so water always moves.

The standard is about ¼ to ½ inch of drop per 10 feet of run. This tool turns that into the actual drop, in inches, over your run — the number you chalk on the fascia before hanging.

Formula

total_drop_in = slope_per_10ft × (run_ft ÷ 10)

The high end starts at the far corner; the low end sits over the downspout. Snap a line from one to the other and hang the gutter to it.

Worked example

A 40-ft run to a single downspout:

  • At 0.25 in/10 ft: 0.25 × (40 ÷ 10) = 1.0 inch total drop.
  • At 0.50 in/10 ft: 0.50 × (40 ÷ 10) = 2.0 inches total drop.

One inch over 40 feet is barely visible to the eye but plenty to keep water moving. If a long eave makes the drop look severe, split it: put a high point in the middle and drain both ways to a downspout at each end — that halves the drop.

Hanging it

  • Not too steep. More than ½ inch per 10 ft starts to look crooked against the fascia and eave line. Stay in the ¼–½ in range.
  • Split long eaves. A 60-ft run with a center high point becomes two 30-ft slopes — smaller drop, better look, and it needs a downspout at each end.
  • Check existing gutters. Water pooling mid-run means it lost its slope — often a sagging hanger. Re-pitch it before you blame the size.
  • Slope does not change length. Order gutter to the horizontal linear feet; the slope drop is a fraction of an inch per foot.

Reference table

Run lengthDrop @ 0.25 in/10 ftDrop @ 0.50 in/10 ft
10 ft0.25 in0.50 in
20 ft0.50 in1.00 in
30 ft0.75 in1.50 in
40 ft1.00 in2.00 in
50 ft1.25 in2.50 in

Total drop, end to end, at the two ends of the standard slope range.

Frequently asked questions

What is the correct slope for a gutter?
About ¼ to ½ inch of drop for every 10 feet of run, pitched toward the downspout. Enough to keep water moving, gentle enough to stay level to the eye.
How much should a 40-foot gutter drop?
At ¼ in per 10 ft, 1 inch total; at ½ in per 10 ft, 2 inches. Snap a chalk line from the high corner to the downspout end and hang to it.
Can a gutter be too steep?
Yes. Past ½ inch per 10 ft it starts to look visibly crooked against the fascia, and water can outrun the outlet. Keep it in the standard range.
What if my run is very long?
Put a high point in the middle and slope both ways to a downspout at each end. That halves the drop and looks better — and it means two outlets instead of one.

Related calculators

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