FIELD CALCULATOR / RISE AND RUN IN FEET
One grade, three ways of saying it.
Read a slope as a percent, a horizontal-to-vertical ratio, or an angle. Enter the measured rise and horizontal run to see equivalent values.
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.
How it works
- Percent = rise ÷ run × 100.
- Ratio = run ÷ rise, written run-to-rise, so a 3:1 slope runs three feet across for every foot up.
- Degrees = the arctangent of rise ÷ run.
- Per foot = rise ÷ run — the drop you would set on a one-foot story pole.
Percent and ratio are not the same scale and do not convert by eye. A 3:1 batter is 33.3%, not 3%. A 2% grade is 50:1. Mixing the two up by a factor of ten is one of the easier ways to build something wrong.
A run of 50 ft that must fall 1 ft: 1 ÷ 50 = 0.02, so 2%. As a ratio that is 50:1, and as an angle 1.15°. Per foot of run it drops 0.02 ft, which is just under a quarter of an inch.
Set that on a 10 ft length and you are looking for 0.2 ft — about 2⅜ inches — between the two ends.
A slope laid back three across for every one up: rise 10 ft, run 30 ft. That is 33.3% and 18.4°. It is the same slope whether the bank is 3 ft tall or 30 ft tall — the ratio does not change with height, only the volume behind it does.
Grades worth recognising on sight
| Percent | Ratio (run:rise) | Degrees |
|---|---|---|
| 1% | 100:1 | 0.57° |
| 2% | 50:1 | 1.15° |
| 8.33% | 12:1 | 4.76° |
| 25% | 4:1 | 14.04° |
| 33.3% | 3:1 | 18.43° |
| 50% | 2:1 | 26.57° |
| 100% | 1:1 | 45° |
These are mathematical conversions. Choose design and excavation slopes from the requirements for your project.
Getting the inputs right
Run is horizontal. If you measured along the face of a bank with a tape, that is slope distance and it is longer than the run. On shallow grades the difference is negligible; on a 2:1 bank it is about 12% and it matters.
Keep your sign convention. This tool treats a positive rise as going up over the run. Pick a direction, stay with it for the whole line, and note which end you started from — a fall of 1 ft is a rise of 1 ft read from the other end.
Percent per hundred, not per foot. A 2% grade falls 2 ft in 100 ft, not 2 ft in 1 ft.
From two rod readings
If you have shot both ends rather than measured a rise directly, the rise is the difference between the two elevations. Work them out with the grade check calculator, subtract, and use the horizontal distance between the points as the run.
Keep it with the job
A slope on its own is a number; a slope recorded against the points it came from is a record. The Driftless Field workspace keeps your grade checks, their benchmarks and tolerances together and prints them as a job report.
Useful on your job?
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