trench volume calculator
Calculate trench volume in cubic feet, cubic yards, gallons, and liters from length, width, and depth for excavation and backfill estimates.
A trench is a straightforward box shape once it’s dug — length, width, and depth are all you need. This calculator converts those three measurements into cubic feet, cubic yards, gallons, and liters, useful for both excavation and backfill planning.
How this calculator works
Trench volume is simply length times width times depth, the same as any rectangular box.
Formula: Cubic feet = length (ft) × width (ft) × depth (ft).
Worked example
A trench 30 ft long, 2 ft wide, and 3 ft deep:
- Cubic feet: 30 × 2 × 3 = 180.00 ft³
- Cubic yards: 180.00 ÷ 27 ≈ 6.667 yd³
- Gallons: 180.00 × 7.48 ≈ 1,346.5 gal
- Liters: 1,346.5 × 3.785 ≈ 5,097.0 L
Reference (30 ft long, 2 ft wide)
| Depth | Cubic feet | Cubic yards |
|---|---|---|
| 1 ft | 60.0 ft³ | 2.222 yd³ |
| 2 ft | 120.0 ft³ | 4.444 yd³ |
| 3 ft | 180.0 ft³ | 6.667 yd³ |
How to measure
Measure the trench length along its run, the width at the bottom (or an average if the sides taper), and the depth from grade to the trench floor. For pricing the dig itself, see the Excavation Cost Calculator, or for backfilling a drain trench with stone, the French Drain Gravel Calculator.
Frequently asked questions
Is a trench just a box shape?
For estimating purposes, yes — most trenches are dug with roughly straight sides and a flat bottom, so length times width times depth gives a close enough volume for material and disposal planning.
What if the trench has sloped sides for safety?
OSHA requires sloped or benched sides for deeper trenches to prevent cave-ins, which makes the top wider than the bottom. For those, measure width at the midpoint depth, or estimate a trapezoidal cross-section separately — the straight-sided box formula will run slightly high in that case.
Does this tell me how much dirt to remove or how much backfill I need?
It gives the volume of the trench itself — that's your excavation (spoil) volume. Backfill volume is usually less than that, since a pipe or utility line and any bedding material take up some of the space.
How much does excavated soil expand when dug out?
Soil typically swells 15-25% in volume once it's loosened from the ground, called the swell factor. So a 180 cubic foot trench might produce 210-225 cubic feet of loose spoil to haul away.
What's a typical trench size for utility lines?
Water and sewer lines are commonly dug 18-24 inches wide and 24-48 inches deep depending on local frost line and code depth requirements. Always check local utility marking and permit rules before digging.
Estimates only. Verify quantities with your supplier before purchasing.