Free construction calculator
Slope and grade calculator
Find the drop you need over a run, or turn a rise and run into inches per foot, percent grade, degrees and a ratio. For drain lines, patios, gutters, ramps and grading.
Result
| Drop over the length | 10"10 in |
|---|---|
| Slope | 0.25" per footAbout 0-1/4" per foot |
| Grade | 2.08% |
| Angle | 1.19° |
| Ratio | 1 : 48 |
- Common targets: drain pipe 3" and under, ¼" per foot; patios away from the house, ⅛" to ¼" per foot; gutters, about ¼" per 10 ft; an accessible ramp, no steeper than 1:12.
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How it works
Slope is rise over run. As a grade: % = rise ÷ run × 100. In inches per foot: rise (in) ÷ run (ft). As an angle: atan(rise ÷ run).
To find the drop you need, multiply the run by the slope: ¼" per foot over 40 ft is 40 × ¼" = 10".
¼" per foot is a 2.08% grade; ⅛" per foot is 1.04%; 1:12 (a ramp) is 8.33%.
Worked example
A 40 ft drain line at ¼" per foot needs 10" of drop end to end: a 2.08% grade, 1.19°.
A 12 ft patio pitched ⅛" per foot away from the house drops 1½" from the wall to the edge.
Questions people ask
What slope does a drain pipe need?
Under the plumbing codes most towns use, ¼" per foot for pipe 3" and smaller, and ⅛" per foot is allowed for larger pipe. Check your local code.
What is ¼ inch per foot as a percent?
2.08%. ⅛" per foot is 1.04%, ½" per foot is 4.17%.
How much should a patio slope?
Most installers use ⅛" to ¼" per foot (1 to 2%) away from the house, so water runs off without the slope being noticeable.
How much slope does a gutter need?
About ¼" for every 10 ft of gutter toward the downspout is the common rule.
What is the maximum slope for a wheelchair ramp?
1:12 under the ADA standards: 1" of rise for every 12" of run (8.33%).
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Built by Northdesk
These calculators are made by Northdesk, construction business software with Dex, an AI assistant, built in.
- Plumbing contractorsA leak at 9 PM, a water heater swap in the morning, rough plumbing on a new build in the afternoon.
- Landscaping contractorsMaintenance routes, patio and wall installs, seasonal crews and a yard full of stone.
- Gutter contractorsLots of small jobs, lots of driving, and customers who need you back every year.
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