Gutter Slope Calculator

This turns a gutter slope into the drop you actually mark on the fascia. Enter the length of the run and the slope in inches per ten feet and it returns the total fall, the drop at every ten foot mark, the slope as a ratio, a percentage and an angle, and whether the gutter still sits on the fascia board once it has fallen that far. A second calculation places the downspouts on a long run and crowns the gutter between them, which halves the fall you have to hide. The slope is an input rather than an assumption because the rules in circulation, a quarter inch per ten feet and a sixteenth of an inch per foot, differ by two and a half times. It says nothing about gutter capacity, which is a separate question from fall.

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Measurements In
The slope goes with it: inches per 10 feet on the first setting, millimetres per metre on the second.
From the high end to the downspout, along one continuous length of gutter, in the unit you chose above.
The usual figure is 1/4 in (0.25) per 10 ft, which is 2.083 mm per metre, and that is what a blank box takes. Use 0.5 in per 10 ft, or 4.167 mm per metre, where it rains hard. Some trade guidance is written as 1/16 in per foot, which is 0.625 in per 10 ft or 5.208 mm per metre.
In inches if you chose feet above, in millimetres if you chose metres. A 5 in K-style gutter has a back about 5 in tall, a 6 in about 6 in. Left blank it takes that 5 in back, which is 127 mm.
The board the gutter hangs on, in inches or in millimetres. A 1x6 fascia measures 5.5 in, a 1x8 measures 7.25 in; the nearest metric boards are 140 mm and 175 mm. Left blank it takes 5.5 in, which is 139.7 mm.
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Measurements In
The slope goes with it: inches per 10 feet on the first setting, millimetres per metre on the second.
In the unit you chose above. A downspout is commonly taken to serve 30 to 40 ft of gutter, which is 9 to 12 m. Left blank it takes 35 ft, or 10 m.
The usual figure is 1/4 in (0.25) per 10 ft, which is 2.083 mm per metre, and that is what a blank box takes. Use 0.5 in per 10 ft, or 4.167 mm per metre, where it rains hard. Some trade guidance is written as 1/16 in per foot, which is 0.625 in per 10 ft or 5.208 mm per metre.
Optional, in square feet if you chose feet above and in square metres if you chose metres. Leave at zero to skip the downspout sizing note.
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