For a straight trench with flat bottom, level top and uniformly sloped sides, measure the top and bottom widths, depth and length. Average the two widths to get a cross-sectional area, then multiply by length.

Formula: cross-section ft² = (top width + bottom width) ÷ 2 × depth; bank yd³ = cross-section × length ÷ 27

Worked example

A 50 ft trench with 3 ft bottom width, 7 ft top width and 4 ft depth has a 20 ft² cross-section: 1,000 ft³ or about 37.04 bank yd³. The sloped sides add about 14.81 yd³ beyond a 3 ft vertical-wall cut.

Widths must describe the same section

This is a constant trapezoid along the entered length. It assumes two straight side faces, a flat bottom and the stated depth everywhere. Split an irregular trench into measured segments and sum them separately; do not average arbitrary end widths into one constant section.

Bank volume comes before swell

The output is in-place excavation volume. It does not include loose swell, compacted fill, pipe displacement or overbreak. The existing excavation swell tool can convert a project-specific bank volume to estimated loose spoil.

Geometry is not a slope design

A top width does not establish a safe excavation. OSHA requires protective systems and soil- and site-specific slope decisions under its excavation standard. This calculator measures a given geometry and does not choose a protective slope or verify compliance.

Explore the related calculation

For a different starting point, try the excavation swell calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

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