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?

On a deep cut it usually does: sloping's extra spoil grows with the square of the depth, and at 4 m (13 ft) in Type C soil the excavation is 13 m (43 ft) wide at the top. Depth and the room you have decide it. The breakdown shows the extra spoil volume that sloping creates over a vertical cut, and at that width a trench box or shoring usually becomes both cheaper and more practical, quite apart from whether the room exists at all.

Heavy Civil & Infrastructure

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.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Excavation depth

Depth from existing ground to the trench bottom.

Capped at 6.096 m (20 ft) here on purpose. Beyond that depth the tabulated slopes do not apply and a protective system must be designed by a registered professional engineer — no table substitutes for that.

Bottom width

Width needed at the base for the work.

Pipe diameter plus working room each side, plus bedding. Bottom width drives spoil volume linearly, so it is worth being deliberate about rather than generous.

Trench length

Run of trench at this profile, for the total excavation volume.

Bank volume — soil measured in place, before it bulks. Loose spoil in the truck runs 10–30% larger; the swell factor lives with the haul-off maths, not here.

Soil type — as classified by a competent person

This calculator does not classify soil. A competent person must.

Classification under OSHA Appendix A requires at least one visual and one manual test, performed on site by a competent person. Previously disturbed ground, submerged soil, soil with water freely seeping in, and material subject to vibration are Type C regardless of what they look like. If nobody has classified it, the answer is Type C.

Excavation top width

19.5 ft

Medium confidence

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 unit length of trench: 3.41 yd³/ft
Extra volume caused by sloping: 2.37 yd³/ft
Top width in feet: 19.5 ft
Total bank excavation volume: 112.44 yd³

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

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

Inputs used

Excavation depth: 8 ft
Bottom width: 3.5 ft
Trench length: 33 ft
Soil type — as classified by a competent person: Type B — 1:1, 45°

Intermediate steps

Setback each side: 8 ft
Slope angle from horizontal: 45 °
Spoil volume per unit length of trench: 3.41 yd³/ft
Extra volume caused by sloping: 2.37 yd³/ft
Top width in feet: 19.5 ft
Total bank excavation volume: 112.44 yd³

Final result19.5 ft

Confidence note: 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.

What this calculation does not cover

Soil classification must be made on site by a competent person using the tests in OSHA Appendix A. This calculator applies the slope for a classification you supply; it cannot make one.
Excavations deeper than 20 feet (6.096 m) require a protective system designed by a registered professional engineer. The depth input is capped for that reason.
Layered soils are classified by the weakest layer present, and previously disturbed ground is Type C regardless of appearance.
Spoil must be kept at least 2 ft (0.6 m) from the edge, and that setback is not included in the top width here. Surcharge from spoil, plant or adjacent structures changes the problem entirely.

The top width is what the excavation costs you at the surface, and it is the figure people are surprised by: in Type C soil a trench 2.4 m deep opens 7.2 m wide before you have dug anything. The section is drawn to one scale on both axes, so the batter you see is the batter the soil classification requires.

Computed in your browser — nothing you enter is uploaded. 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.

Sources checked 2026-08-27 · in the site-wide review of 2026-09-06 · v1.1.0

Regulatory standards & verification citations3

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

Cite this page

Your workspace

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.

Tools and safety for this job

To excavate by hand and excavate by machine. Generic types, no brands, no prices.

Protection this work requires

Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
Digging blind strikes gas, water and power every day: get the plans, scan with a cable avoidance tool, and hand-dig trial holes over anything you find.

Excavate by machine: Operating an excavator is a trained and, in most markets, formally certified activity, and hiring one does not include that training. Underground services must be traced before any machine dig. This list covers the tools, not the competence.

Show the 6 tools this job needs

Essential

Cable and pipe detector
Shovel and spade
Tape measure
Wheelbarrow

Recommended

Spirit level
String line and pins

what each groundwork tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Digging Without Hitting a Buried Serviceuses this calculator
Most strikes happen on holes too small to feel like excavation — so here is the records, scan, trial hole and machine-margin sequence in full.
Sizing a Septic Drain Fielduses this calculator
Every dimension of a septic drain field descends from one measured percolation rate — how to take it, defend it, and protect it on site.
Trench Safety and Supportuses this calculator
Soil classification is the design input for every trench — it sets the batter, the bench and the shield, and it changes mid-dig more often than crews expect.

Called something else where you work? Trench support — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Sloping vs Shoring an Excavation — the factors that actually differ, with no invented prices.

How to calculate trench sloping & excavation width in 5 steps

Excavation depthDepth from existing ground to the trench bottom.
Bottom widthWidth needed at the base for the work.
Trench lengthRun of trench at this profile, for the total excavation volume.
Soil type — as classified by a competent personThis calculator does not classify soil. A competent person must.
Excavation top widthThe tool computes the excavation top width from those figures and shows the formula, its sources, and a confidence rating alongside it.

Excavation top width by excavation depth

Page defaults, not your figures above.

Excavation depth	Excavation top width (ft)
4 ft	11.3
6 ft	15.3
8 ft	19.3
10 ft	23.3
12 ft	27.3
14 ft	31.3

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?: On a deep cut it usually does: sloping's extra spoil grows with the square of the depth, and at 4 m (13 ft) in Type C soil the excavation is 13 m (43 ft) wide at the top. Depth and the room you have decide it. The breakdown shows the extra spoil volume that sloping creates over a vertical cut, and at that width a trench box or shoring usually becomes both cheaper and more practical, quite apart from whether the room exists at all.

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.