Gutter Drop CalculatorFree online other calculator — instant results, no sign-up
Find total vertical fall from gutter length and slope.
Sign in to save results and favorites.
About the Gutter Drop Calculator
The Gutter Drop Calculator finds the total vertical fall needed along a gutter run from its length and specified fall per meter. Use it to determine how much lower the downstream end should be than the upstream end when setting a constant gutter slope.
- Run length (m)
- The horizontal length of the gutter section over which the fall is applied, measured in meters.
- Fall per meter (mm/m)
- The specified vertical drop for each meter of gutter run, measured in millimeters per meter.
Formula and method
D = L × s; with the default inputs, D = 10 m × 3 mm/m = 30 mm.
- DTotal vertical fall from the upstream end to the downstream end, in millimeters.
- LHorizontal gutter run length, in meters.
- sSpecified fall per meter of gutter run, in millimeters per meter.
Multiply the run length by the fall per meter. The meter units cancel, leaving the total vertical fall in millimeters. For the default run length of 10 m and fall per meter of 3 mm/m, the result is 30 mm.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Run length10 m
- Fall per meter3 mm/m
Results
- Result30 mm
How to use the Gutter Drop Calculator
- 1Identify the gutter section that slopes continuously from a high point toward an outlet.
- 2Enter its horizontal run length in meters; the default is 10 m.
- 3Enter the specified fall per meter in mm/m; the default is 3 mm/m.
- 4Read the calculated total fall; the default inputs produce 30 mm.
- 5Use that fall as the required height difference between the section’s ends, checking the installation against manufacturer guidance and local requirements.
Reading your result
The Result row shows the total vertical fall in millimeters, not the fall per meter. A result of 30 mm means the downstream end should be 30 mm lower than the upstream end across the entered 10 m run. It does not specify either end’s absolute installation height.
Limitations
The calculation assumes a constant slope along one continuous run and uses horizontal run length. It does not determine the appropriate slope, drainage capacity, gutter size, outlet size, or bracket spacing, and it does not account for sagging or installation tolerances. The default slope is an example, not a universal recommendation. Check manufacturer instructions and applicable local requirements, and calculate sections separately where slope direction changes.
Common questions
Why do the default inputs give a gutter drop of 30 mm?+
A fall of 3 mm for each meter across a 10 m run gives 10 × 3 = 30 mm of total vertical fall.
Should I enter the whole gutter length if it slopes toward outlets at both ends?+
No. If the gutter has a central high point, calculate each run from that high point to its outlet separately, using the length and specified slope for that section.
Does 3 mm/m mean a 3 percent gutter slope?+
No. A meter contains 1,000 mm, so 3 mm/m is a slope ratio of 3/1,000, or 0.3 percent.
Does the calculated drop guarantee that my gutter will drain adequately?+
No. The result only establishes the end-to-end height difference for the entered slope. Drainage also depends on rainfall, roof catchment area, gutter and outlet capacity, debris, and whether the installed gutter maintains a consistent fall.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
You might also like
Concrete Calculator
Concrete volume and bags for a slab.
BTU Calculator
Heating/cooling BTUs for a room.
Square Footage Calculator
Area in square feet and meters.
Stair Calculator
Number of steps, riser and tread for stairs.
Roofing Calculator
Roof area and shingle bundles.
Tile Calculator
Tiles needed for a floor or wall.
Results are estimates for informational purposes and are not financial, medical or legal advice.