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Earthwork

Trench Volume Calculator

Three measurements, three answers. Enter the length, width and depth of a trench in any combination of units and get the volume in cubic feet, cubic yards and cubic meters — the numbers you need for spoil, backfill or bedding quantities.

Your measurements

Results update as you type. Every unit dropdown converts for you.

Trench volume

8.89cubic yards

Volume in cubic feet
240.0 cu ft
Volume in cubic meters
6.80 m³
Dimensions used
40.00 × 2.00 × 3.00 ft
Show the calculationOpen
  1. Volume40.00 ft × 2.00 ft × 3.00 ft=240.0 cu ft
  2. Convert to cubic yards240.0 ÷ 27=8.89 cu yd
  3. Convert to cubic meters240.0 × 0.0283168=6.80 m³

Reading your result

Cubic yards is the headline because that is how spoil haulage and backfill are sold and quoted. Cubic feet is there for smaller jobs and for feeding into the material calculators.

This is the in-place volume — the size of the hole as dug. It is not the size of the pile that comes out of it, which will be larger once the soil loosens.

For backfill planning, subtract whatever will occupy the trench: pipe, bedding, and any stone envelope. The remainder is what you need to bring back or bring in.

How this calculator works

A trench with straight sides and a flat bottom is a rectangular box, so the volume is simply length times width times depth.

Everything is converted to feet before multiplication, so you can enter length in feet, width in inches and depth in meters without doing any conversion yourself.

Cubic yards come from dividing cubic feet by 27, since a cubic yard is 3 × 3 × 3 feet. Cubic meters use the exact 0.0283168 conversion.

This is the in-place volume — the hole as dug. Soil expands once it is loose, so if you are estimating truck loads or stockpile size, run the number through the excavation volume calculator and add a swell allowance.

The formula

Volume
length × width × depth
Cubic yards
cubic feet ÷ 27
Cubic meters
cubic feet × 0.0283168

Worked example

A 40 ft trench, 24 inches wide and 36 inches deep.

  1. 01Convert width24 in ÷ 12=2 ft
  2. 02Convert depth36 in ÷ 12=3 ft
  3. 03Volume40 × 2 × 3=240 cu ft
  4. 04Cubic yards240 ÷ 27=8.89 cu yd
  5. 05Cubic meters240 × 0.0283168=6.80 m³

The trench holds about 8.9 cubic yards in place — roughly one full tandem load of spoil once it is dug and loosened.

How to take the measurements

  • Measure length along the centerline, following the route rather than the straight-line distance between endpoints.
  • Use the average width if the trench flares. Measure at the top and bottom and take the midpoint.
  • Measure depth from finished grade to the trench bottom, at several points if the ground is uneven, and average them.
  • Split trenches that change dimensions into separate sections and total the results.
  • For bedding or backfill quantities, subtract the volume taken up by pipe and any stone envelope.

Practical considerations

  • Machine-dug trenches are close to rectangular; hand-dug ones flare at the top. Averaging the top and bottom widths gets you much closer than measuring either alone.
  • Where depth changes along the run — a trench that starts shallow and deepens to hold grade — split it into sections and total them rather than averaging the ends.
  • If you are hiring haulage, ask whether the quote is by volume or by weight. Volume needs the loose figure from the excavation calculator; weight needs the soil weight calculator.
  • Spoil has to go somewhere while the trench is open. A 40 ft trench three feet deep produces a pile that is awkward to place on a small lot.

Assumptions and limitations

  • The calculation assumes vertical walls and a flat bottom. Battered or benched walls hold considerably more volume than the nominal dimensions suggest.
  • In-place volume only. Swell on excavation and compaction on backfill both change the number, in opposite directions.
  • Trench safety, shoring and sloping requirements are outside what a volume figure can tell you.

Frequently asked questions

How many cubic feet are in a cubic yard?

Twenty-seven. A cubic yard measures three feet on each side, and 3 × 3 × 3 is 27.

Why does my spoil pile look bigger than the trench?

Because digging loosens soil and introduces air. Depending on the material, loose volume typically runs 10% to 40% above in-place volume. The excavation volume calculator applies that swell for you.

What if my trench has sloped sides?

Use the average of the top and bottom widths. That gives the exact volume for a trench with evenly sloped sides and a very close estimate for anything less tidy.

How do I estimate backfill after the pipe goes in?

Take the trench volume, then subtract the pipe volume and any stone bedding. The French drain gravel calculator does the pipe subtraction for you.

Should I use the top width or the bottom width?

The average of the two. That gives the exact volume for evenly sloped walls and a close estimate for anything less tidy.

How much backfill will I need to bring in?

Start from this volume, subtract the pipe and any stone, then add an allowance for compaction. Excavated soil rarely fills its own trench back to grade once it is compacted properly.

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