Calculate gutter slope, drop needed, or run from drop using gutter length and pitch in feet, inches, millimeters, centimeters, or percent.
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Gutter Slope Formula
The calculator uses three rearrangements of the same slope relationship, depending on which tab you choose.
Drop = Run × Pitch Pitch = Drop ÷ Run Run = Drop ÷ Pitch
- Drop = vertical height difference between the high end and the downspout end (inches)
- Run = horizontal length of the gutter to the downspout (feet)
- Pitch = slope expressed as inches of fall per foot of run (in/ft)
All inputs are converted to inches and feet internally before calculating, then converted back to your chosen units. Grade percentage is computed as (pitch ÷ 12) × 100.
Typical Pitch Values and Drop Reference
Most gutter installs target a slope between 1/4 in per 10 ft and 1/16 in per ft. Use these tables to sanity-check your result.
| Pitch | In/ft | Grade | Use |
|---|---|---|---|
| 1/4 in per 10 ft | 0.025 | 0.21% | Minimum standard slope |
| 1/2 in per 10 ft | 0.05 | 0.42% | Heavy rainfall regions |
| 1/16 in per ft | 0.0625 | 0.52% | Common residential pitch |
| 1/8 in per ft | 0.125 | 1.04% | Steep, fast-draining |
| Run length | Drop at 1/4 in per 10 ft | Drop at 1/16 in per ft |
|---|---|---|
| 10 ft | 1/4 in | 5/8 in |
| 20 ft | 1/2 in | 1 1/4 in |
| 30 ft | 3/4 in | 1 7/8 in |
| 40 ft | 1 in | 2 1/2 in |
| 50 ft | 1 1/4 in | 3 1/8 in |
Example and FAQ
Example: A 32 ft gutter draining to one downspout at 1/4 in per 10 ft needs a drop of 32 × 0.025 = 0.80 in. Mark the high end about 13/16 in above the downspout end.
What if the run drains to two downspouts? Slope each section toward its own downspout from a high point in the middle. Use the section length, not the total gutter length, as your run.
Is more slope always better? No. Steeper than 1/8 in per ft drains quickly but looks visibly tilted next to the fascia and roofline.
How do I measure existing slope? Use the Check slope tab. Hold a level at the high end of the gutter, measure straight down to the gutter at the downspout end, and enter that drop with the run length.
