Free tool · Measure
Slope Calculator: Percent, Degrees and 1 in N
Work out a slope from rise and run or two levels, and convert between percent, degrees and 1 in N — for roads, drains, ramps and roofs.
Free · no sign-up · works in your browser, on phone and computer
Example · A drain run
- Levels
- 45.260 at the start, 44.810 at the end, 30 m apart
- Percent
- -1.5 %
- Degrees
- -0.859°
- 1 in N
- 1 in 66.7 (falling)
What it does
From what you measured
Rise and run, or two levels and the distance between them.
Three ways to write it
Percent grade, angle in degrees and 1 in N, always side by side.
Convert any one
Type a percent, an angle or a 1 in N and get the other two.
Slope length
The length along the slope, and whether it rises or falls.
How to use it
- 1
Press Use the tool.
- 2
Type the rise and run, two levels and a distance, or a slope to convert.
- 3
Read the slope as percent, degrees and 1 in N.
Who it's for
- Site engineers setting drain and pipe falls
- Builders and architects checking ramps and roofs
- Road and earthworks crews checking crossfall and batters
Three ways to write the same slope
- Percent (grade): rise ÷ run × 100. A 1 m rise over 50 m is 2%. Used for roads, drains and pipes.
- Degrees: the angle from level, arctan(rise ÷ run). 45° is 100%.
- 1 in N: how far you go along for each unit up. 2% is 1 in 50. Used for ramps and falls.
Typical values
- Wheelchair ramp: no steeper than 1 in 12 (8.3%) in most codes, 1 in 20 (5%) preferred.
- Foul drain, 100 mm pipe: about 1 in 40 to 1 in 80 (2.5% to 1.25%).
- Road crossfall: about 2.5%.
Always check the code or specification for your job; these are only rough guides.
Levels along the whole line
Need the level at every chainage, the profile, crossfall and an Excel or PDF report? Use Slope Calculator, our free app for the browser and Windows.
Questions
How do I work out a slope percentage?
Rise ÷ run × 100. A 1.5 m rise over 60 m is 2.5%.
How do I convert percent to degrees?
Degrees = arctan(percent ÷ 100). 100% is 45°, 10% is about 5.71°.
What does 1 in 12 mean?
One unit up for every 12 along — 8.33%, about 4.76°. It is a common maximum for wheelchair ramps.
What fall does a drain need?
Often about 1 in 40 to 1 in 80 for a 100 mm foul drain, but always follow the code or specification for your job.
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Got a whole sheet of points?
Open the web app in your browser, or install the Windows app to work offline. Both are free, with no point limit.