FREE FIELD CALCULATOR
Slope and grade calculator
Turn a measured rise or fall and horizontal distance into percent grade, a slope ratio and degrees.
What you’ll need
- The elevation change between the two ends, with a minus if it falls
- The horizontal distance between them, not the tape along the slope
- Which end you’re measuring from
Enter a rise and a run.
You will get percent, a run-to-rise ratio, the angle in degrees, and the drop per foot of run.
Try it with these numbers
- For a line falling 1 ft over 50 ft, enter rise or fall -1 and horizontal run 50.
- Calculate. Expect -2%, a 50:1 horizontal-to-vertical ratio and about -1.15°.
- Read the direction as falling from your start point. Over 10 horizontal feet, that grade falls 0.20 ft.
- For a 3:1 bank, try rise 10 and run 30. Expect about 33.33%, not 3%.
Reading your result
Percent is the vertical change per 100 horizontal units. Ratio tells you horizontal distance for one unit vertically. The sign and direction show whether the line rises or falls.
Use the format shown on your plans. A 2% grade and a 2:1 slope are very different things. The diagram helps explain the direction; the values come from your measurements.
Where this goes wrong on site
- Reading a ratio backwards. OSHA writes excavation slopes horizontal to vertical: Type A soil ¾:1, Type B 1:1, Type C 1½:1. A 1½:1 slope read correctly is 66.7%; read as vertical-to-horizontal it becomes 150%.
- Mixing the two conventions on one job. ADA writes its limits the other way, as rise to run: ramps no steeper than 1:12 (8.33%), cross slope no more than 1:48 (about 2.08%), and a walking route steeper than 1:20 (5%) counts as a ramp. Check which convention each drawing uses.
- Using the tape distance along a slope as the horizontal run.
- Dropping the minus sign and reversing a drainage fall.
- Subtracting two rod readings from different instrument setups as though they share one HI.
Sources: OSHA 29 CFR 1926 Subpart P, Appendix B · U.S. Access Board guide to ADA ramps
How the math works
Percent = rise ÷ horizontal run × 100. H:V ratio = run ÷ absolute rise. Angle = atan(rise ÷ run). A level line has zero percent and angle; its ratio is shown as Level.
Keep the number with the job
Calculate above, then download a Letter or A4 PDF, copy the result or share it from your phone. The result sheet keeps your inputs and assumptions. Changing an input means you need to calculate again before exporting. For a pipe run, carry that grade into the pipe invert station table.
Open the private field workspace for saved jobs and reports across your phone and computer, or read the free-calculator guide. Tell Jesse what would make this easier on your job.
Useful on your job?
Share this free calculator with someone who could use it, or tell Jesse what needs improving.
Shares the tool link only, without your measurements. https://driftlesssolutions.us/tools/slope-grade/