Gutter Slope Calculator
Enter the gutter length and slope percentage to calculate the fall (height difference) and slope ratio, and check it meets the minimum roof-gutter drainage slope.
Input Data
Results
At a glance:Gutter drainage slope is expressed as a percentage: units dropped per 100 horizontal units. Fall = length (m) × slope% × 10 (to mm). Slope ratio = 1 : (100 ÷ slope%). To avoid ponding and moss, roof gutters and open channels commonly use a minimum slope of about 0.5% (1:200); too flat ponds water, too steep looks poor and is hard to build. This calculator uses 0.5% as the common minimum check value.
Formula
Fall (mm) = length (m) × slope% × 10
Slope ratio = 1 : (100 ÷ slope%)
Pass condition: slope% ≥ 0.5
$$f = L\times p\times 10$$$$R = 1 : \frac{100}{p}$$$$p \ge 0.5\%$$How to Use
- Enter the horizontal gutter length (m).
- Enter the slope percentage (roof gutters commonly 0.5–1%).
- The tool outputs the fall, slope ratio and check result.
Case Studies
Pitched-roof eave gutter
6 m, slope 1%.
Fall 60 mm, slope ratio 1:100, meets the ≥0.5% drainage requirement.
Terrace open channel
4 m, slope 0.3%.
Fall 12 mm, slope ratio 1:333, below 0.5%, increase the slope.
FAQ
How is gutter slope different from floor drainage slope?
Floor drainage (drainage-slope) is for indoor waterproofed floors and usually ≥1.25%; gutters are roof/exposed channels where a minimum of about 0.5% is enough — different scenarios.
Why set a minimum slope?
Too flat a gutter drains slowly and ponds water, growing moss and leaking, so a minimum slope ensures self-draining.
Related Tools
References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.