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Trench Sloping & Excavation Width Calculator

Top width and spoil volume for a sloped excavation, at the maximum allowable slope for a soil type a competent person has classified.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax
33 ft3.5 ft8 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Excavation top width

19.5 ft

Check your inputs

Geometry at the tabulated maximum allowable slope for the soil type you selected. It is not a classification, and it is not a protective-system design.

Setback each side
8 ft
Slope angle from horizontal
45 °
Spoil volume per metre of trench
8.55 m³/m
Extra volume caused by sloping
5.95 m³/m
Top width in feet
19.5 ft
Total bank excavation volume
112.44 yd³

Running these inputs gives 19.5 ft as the excavation top width. Top width in feet carries the most weight in this calculation, at 19.5 ft. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States — pick a different market above and the figures re-cast accordingly.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • OSHA 29 CFR 1926 Subpart P, Appendix B — maximum allowable slopes for excavations less than 20 feet deep: Stable Rock vertical; Type A 3/4:1 (53°); Type B 1:1 (45°); Type C 1½:1 (34°)
  • 29 CFR 1926.652 — excavations deeper than 20 feet require a protective system designed by a registered professional engineer
  • Soil classification under Appendix A must be performed by a competent person using at least one visual and one manual test

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why will this not tell me my soil type?
Because classification is the safety-critical judgement, and it cannot be made from a web form. OSHA requires a competent person on site to perform at least one visual and one manual test — thumb penetration, pocket penetrometer, plasticity — and to reassess as conditions change. A dropdown that guessed would be dressing up the dangerous half of the problem as the easy half. Where nobody has classified it, the correct assumption is Type C.
What automatically makes soil Type C?
Previously disturbed ground — anything backfilled before. Submerged soil, or soil with water freely seeping in. Soil in a layered system sloping into the excavation at four horizontal to one vertical or steeper. And soil subject to vibration from traffic or plant. Any of these overrides what the material appears to be.
Why is the depth capped at 20 feet?
Because the OSHA slope tables stop there. Beyond 6.096 m the protective system must be designed by a registered professional engineer for the specific conditions — there is no table that extends, and extending one by extrapolation is exactly the kind of false confidence that gets people killed in trenches.
Does sloping cost more than shoring?
It depends on depth and on the room you have. The breakdown shows the extra spoil volume that sloping creates over a vertical cut, and it grows with the square of depth — at 4 m in Type C the excavation is 13 m wide at the top. That is the point at which a trench box or shoring usually becomes both cheaper and more practical, quite apart from whether the room exists at all.