Sloping is the simplest protective system, but the footprint grows fast with depth and weaker soil. This calculator applies the maximum allowable slopes from Appendix B to Subpart P for excavations 20 feet deep or less.
How the calculation works
- Setback per side = depth × the horizontal part of the slope ratio (0 for stable rock, 0.75 for Type A, 1 for Type B, 1.5 for Type C).
- Top width = bottom width + 2 × setback.
- Spoil distance = setback + 2 feet, measured from the edge of the trench bottom, so spoil sits at least 2 feet beyond the top of the slope (1926.651(j)(2)).
- Volume = length × depth × average of top and bottom width, divided by 27 to get cubic yards.
| Soil | Max slope | Angle | Setback for a 10 ft deep cut |
|---|---|---|---|
| Stable rock | Vertical | 90° | 0 ft |
| Type A | ¾:1 | 53° | 7.5 ft |
| Type A short-term | ½:1 | 63° | 5 ft |
| Type B | 1:1 | 45° | 10 ft |
| Type C | 1½:1 | 34° | 15 ft |
Limits of this calculator
- It doesn't classify soil. A competent person must do that with at least one visual and one manual test. See soil classification.
- Slopes over 20 feet need a registered professional engineer's design.
- Surcharge loads and signs of distress call for flatter slopes. Tick the distress box to see the minimum ½:1 flattening.
- Layered soils are governed by the weakest layer, and benching follows the figures in Appendix B.
Learn the full method in the free sloping and benching lesson.
Sources and official references
Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1926 Subpart P. It does not replace the site-specific training and competent person your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.