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.
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.
More free tools
- Distance and bearingThe distance and bearing between two points from latitude and longitude on the WGS 84 ellipsoid, or from eastings and northings on a grid — plus the point at a given bearing and distance.
- Plot area from coordinatesPaste the corners of a plot as eastings and northings or latitude and longitude and get its area in m², hectares, acres, kanal and marla, with the perimeter.
- Coordinates on a mapClick the map, search a place or use your location to get its latitude and longitude, degrees-minutes-seconds, UTM zone and easting/northing, with a Google Maps link.
- DMS ↔ decimal degreesConvert degrees, minutes and seconds such as 25°11'35"N to decimal degrees and back — one value or a whole list pasted from Excel.
- Lat/long ↔ UTMConvert latitude and longitude to UTM easting, northing and zone on WGS 84, or UTM back to latitude and longitude. The zone is worked out for you.
- Land area unitsConvert land and floor areas between square metres, square feet, acres, hectares, kanal, marla, feddan, dunam, guntha and cents.
Got a whole sheet of points?
Open the web app in your browser, or install the Windows app to work offline with no point limit. Both are free.