Trench Volume Calculator

Calculate the volume of soil to excavate for a trench — pipeline, drainage, or cable-laying jobs.

Trench volume = length × width × depth. A 50 m trench, 0.6 m wide and 1.2 m deep contains 36 m³ of material to excavate.

Calculator

Trench length (m)Trench width (m)Minimum working width — allow 300–450 mm clearance each side of the pipe OD.Trench depth (m)Average depth from surface to invert — include pipe OD and bedding allowance.

Excavation volume

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How it works

A rectangular trench is the standard excavation shape for pipelines, drainage, and cable routes. Multiply the three dimensions to get in-situ volume. For disposal, multiply by the swell factor (1.2–1.4 for clay, 1.1 for sandy soil) to find the loose volume that will fill trucks or skip bins.

Worked example

50 m × 0.6 m × 1.2 m = 36 m³ in-situ. At a swell factor of 1.25 for stiff clay, that becomes 45 m³ loose — roughly 4–5 × 10 m³ skip loads, or about 72 t of spoil at 1,600 kg/m³.

Assumptions & limitations

Assumes a uniform rectangular trench with vertical walls. For benched or battered walls, calculate each section separately. In-situ volume is always less than loose spoil volume — apply a swell factor when estimating haulage or disposal costs. Excavations deeper than 1.5 m require a safe system of work under AS 2601 and state WHS regulations.

Frequently asked questions

What width should I allow for a pipe trench?

The minimum safe working width is the pipe outer diameter plus 300 mm clearance each side for bedding compaction. For a 150 mm OD pipe, allow 0.6–0.75 m. Deeper trenches may need additional width for shoring frames or battered walls.

How do I convert excavation volume to tonnes?

Multiply in-situ volume by the soil bulk density: sandy soil ~1,500 kg/m³, clay ~1,600–1,800 kg/m³, rock ~2,200 kg/m³. For 36 m³ of clay at 1,650 kg/m³: 36 × 1.65 = 59.4 t.

What is a swell factor and why does it matter?

When soil is excavated it loosens and takes up more space — typically 10–40% more depending on soil type. Swell factor = loose volume ÷ in-situ volume. Always use it when sizing skip bins or estimating truck loads: loose volume = in-situ volume × swell factor.

At what depth do I need trench shoring?

In most Australian states, excavations deeper than 1.5 m require a formal safe system of work — shoring, trench box, or battered walls — under AS 2601 and state WHS legislation. Always check local requirements and soil conditions before excavating.

Last updated 22 June 2026

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