How many cubic yards is 100 feet of trench?

It depends entirely on the section. A 100 ft run at 12 in wide and 3 ft deep is 300 cu ft, or 11.1 cu yd. The same 100 ft at 24 in wide and 5 ft deep is 1,000 cu ft, or 37 cu yd. Enter your own section above rather than working from a rule of thumb.

Do I subtract the pipe from the excavation?

Not from the excavation — you still have to dig it. You subtract it from the backfill, because the pipe occupies volume that would otherwise need filling. This calculator reports both figures separately for that reason.

Why is my spoil more than my excavation?

Because excavated soil bulks up. A cubic yard measured in the ground occupies noticeably more than a cubic yard once it is loose in a truck. Enter your swell factor and the spoil figure will reflect it.

Earthwork · Trench and spoil volume

Trench Excavation Calculator

Spoil, backfill and bedding quantities for a run of trench — from the cross-section up. How it works

Trench Volume

Try an example

Excavated volume

cubic yards

Bank measure

Trench cross-section, to scale

250 ft run · vertical walls

Cross-section area: 10ft²
Total linear feet: 250ft
Cubic metres: 70.79m³

Vertical walls at 5 ft or deeper: a trench people enter at that depth normally needs sloping, benching or a protective system. Model the batter you will actually cut, or the volume here will be well under the real quantity.

Show the calculation3 steps

The working

Section area = Width × Depth
= 2 ft × 5 ft
= 10 ft²
Volume = Section area × Total length
= 10 ft² × 250 ft
= 2,500 cu ft
Cubic yards = Cubic feet ÷ 27
= 2,500 ÷ 27
= 92.59 cu yd

A trench is a cross-section repeated along a length, so everything follows from the shape of that section. Enter the bottom width and depth, lay the walls back if they are battered, and the calculator returns the excavated volume, the spoil once it swells, and the backfill left over after the pipe and bedding take their share.

How this calculator works

Only your inputs and exact unit conversions. Where a figure comes from anywhere else, it is recorded below with its source.

Specification

Formula version: 1.0.0
Last reviewed: 2026-08-14
External data: None
Category: Earthwork

No benchmark, average or market figure is built into this tool. How we calculate

What this calculates

The excavated volume of a trench, plus the quantities that follow from it: spoil after swell, bedding material to import, and backfill left over once the pipe and bedding occupy part of the section.

The cross-section is the whole calculation

A trench is one shape repeated along a run, so the volume is simply the cross-sectional area multiplied by the length. With vertical walls that area is width × depth. With battered walls it is a trapezoid: the bottom width, the top width, averaged, times the depth — which simplifies to d × (w + s·d) where s is the side slope ratio.

Because the slope term is multiplied by the depth twice, laying the walls back adds volume quadratically. A 5 ft trench cut at 1:1 has more than double the section of a vertical one with the same bottom width.

Pipe and bedding

Pipe volume is π × D² ÷ 4 × length, using the outside diameter. Bedding is treated as a layer of the bottom width across the full run. Both are subtracted from the excavation to give the backfill quantity, on the assumption that the trench is refilled to grade.

Spoil versus backfill

These are different numbers and confusing them is a common source of surprise haulage bills. Spoil is what comes out, expanded by swell. Backfill is what has to go back in, measured in place. If you are not reusing the excavated material you are paying to haul the spoil away and paying again to import the backfill.

250 ft of trench, 24 in wide, 5 ft deep, vertical walls

Given

Length: 250 ft
Bottom width: 24 in (2 ft)
Depth: 5 ft

Step by step

01Section area= 2 ft × 5 ft= 10 sq ft
02Volume= 10 sq ft × 250 ft= 2,500 cu ft
03Cubic yards= 2,500 ÷ 27= 92.6 cu yd

Excavated volume

92.6 cubic yards

What it assumes

01The cross-section is constant over the whole run and the ground surface is level.
02Side slopes, when entered, are equal on both sides.
03Bedding is modelled as a rectangular layer of the bottom width.
04Backfill is measured as in-place volume, before any compaction allowance.

What it does not do

Manholes, chambers, thrust blocks and bell holes are not included — add them separately.
Varying depth along the run is not modelled. Split the run into sections of similar depth.
Shoring and trench box requirements are a site-safety determination and are outside the scope of this tool.

Common questions.

How many cubic yards is 100 feet of trench?: It depends entirely on the section. A 100 ft run at 12 in wide and 3 ft deep is 300 cu ft, or 11.1 cu yd. The same 100 ft at 24 in wide and 5 ft deep is 1,000 cu ft, or 37 cu yd. Enter your own section above rather than working from a rule of thumb.
Do I subtract the pipe from the excavation?: Not from the excavation — you still have to dig it. You subtract it from the backfill, because the pipe occupies volume that would otherwise need filling. This calculator reports both figures separately for that reason.
Why is my spoil more than my excavation?: Because excavated soil bulks up. A cubic yard measured in the ground occupies noticeably more than a cubic yard once it is loose in a truck. Enter your swell factor and the spoil figure will reflect it.

Behind the numbers

The methods and definitions this calculator applies, explained in full and with their sources.

GuideHow to calculate trench volumeTrench volume is the cross-section times the length. Vertical and sloped walls, why laying the walls back adds volume quickly, and how spoil and backfill differ from the excavation.

Where people go next

All earthwork tools

Ordered by what usually comes next in the same job, not by keyword.

01Trenching CostCost per foot and totalPrice a run of trench per linear foot, per cubic yard or by the hour — with backfill, bedding and restoration.02ExcavationBank volume in cubic yardsCubic yards of material to be dug out — including battered side walls, over-excavation and swell.03Dirt HaulingTruck loads and round tripsTruck loads, haul time and cost — including whether your trucks fill up by volume or by weight first.04Cubic YardCubic yards from any shapeCubic yards from length, width and depth, from a square-foot area and a depth, or from a volume you already have in cubic feet or metres.