Reading the ratio
A slope ratio compares the rise to the run. 1V:2H means the ground rises, or falls, 1 unit vertically for every 2 units horizontally. The units don't matter as long as they're the same: 1 m in 2 m and 0.5 m in 1 m are the same slope.
The catch is the order. Some drawings and specifications put the vertical first (1V:2H), others put the horizontal first (2H:1V, or just 2:1), and "1 in 2" is common too. Even our own apps differ: TrenchCalc asks for a batter as H:V, while SlopeCheck shows the slope as V:H. Always check which number is the vertical, and label both when you write one down.
Converting a ratio to degrees and percent
For a slope of 1 vertical to H horizontal:
- Angle = arctan(1 ÷ H)
- Grade (%) = 1 ÷ H × 100
- H from an angle = 1 ÷ tan(angle)
| Ratio (V:H) | Angle | Grade |
|---|---|---|
| 1V:1H | 45.0° | 100% |
| 1V:1.5H | 33.7° | 66.7% |
| 1V:2H | 26.6° | 50% |
| 1V:3H | 18.4° | 33.3% |
| 1V:4H | 14.0° | 25% |
| 1V:10H | 5.7° | 10% |
| 1V:20H | 2.9° | 5% |
| 1V:50H | 1.1° | 2% |
Note that a 100% grade is a 45° slope, not a vertical wall.
Worked examples
- A batter falls 1.5 m over a horizontal distance of 3.0 m. That's 1.5:3.0, or 1V:2H, which is 26.6° or a 50% grade.
- An inclinometer reads 18° on an embankment. H = 1 ÷ tan(18°) = 3.08, so the slope is about 1V:3.1H.
Measuring a slope on site
- String line, level and tape: run a level string line out from the top of the slope, then measure the horizontal distance along the string and the drop from the string to the ground at the end. Rise over run gives the ratio.
- Digital level or inclinometer: lay a straight edge along the slope, read the angle off it, and convert.
- Survey: levels at the top and the toe, and the horizontal distance between them.
- A phone with LiDAR: quick checks with an app like SlopeCheck, which reads the slope in front of you as a ratio.
Measure over a length that represents the slope, not a single bump or hollow. Phone and app readings are field estimates. They're fine for a quick check, but not a substitute for a survey where the result matters.
A note on safety
This article is about reading and converting slopes. The slope an excavation, batter or embankment can safely stand at depends on the ground and the conditions. It should come from your engineer or geotechnical advice and your work health and safety obligations.