What is the minimum slope for gutters

As a general rule, gutter slope is set at 1/2 inch per 10 feet of guttering. For example, if you have 30 feet of guttering, the calculation is 1/2 x 3 = 1.5 inches. This means the downspout end of the gutter should be set 1 1/2 inches lower than the other end.

To calculate gutter slope, attach one end of a long piece of string to the highest point of your gutter and the other end at the location of your downspout.

Use a string level to ensure the string is completely parallel to the ground. Measure the length of the string to determine the distance between the two points. If you have 30 feet of guttering, as above, you know the slope should be 1 1/2 inches.

Take the downspout end of the string, lower it 1 1/2 inches, and reattach it.

Mark both ends of the string with a pencil then remove it. Snap a chalk line from these two marks to determine the line your gutters will follow. Repeat this process for all gutters around your roofline.