trench volume calculator
A trench volume calculator multiplies length × width × depth: a 30 × 2 × 3 ft trench is 180 cubic feet, or 6.667 cubic yards of soil to dig out.
Trench volume calculator formula
A trench volume calculator multiplies the three dimensions of the trench. The formula is volume in cubic feet = length × width × depth, with all three in feet.
Divide by 27 to get cubic yards. The calculator also returns gallons (cubic feet × 7.48052) and liters (cubic feet × 28.3168), which help when the trench holds water or a tank. The default trench is 30 ft long, 2 ft wide and 3 ft deep.
Worked examples
Example 1 is the default trench, 30 ft × 2 ft × 3 ft.
- Cubic feet: 30 × 2 × 3 = 180
- Cubic yards: 180 ÷ 27 = 6.667
- Gallons: 180 × 7.48052 = 1,346.5
- Liters: 180 × 28.3168 = 5,097.0
Example 2 is a longer line, 120 ft × 1.5 ft × 4 ft.
- Cubic feet: 120 × 1.5 × 4 = 720
- Cubic yards: 720 ÷ 27 = 26.667
- Gallons: 720 × 7.48052 = 5,386.0
- Liters: 720 × 28.3168 = 20,388.1
The second trench is 26.7 cubic yards of undisturbed soil. After it is dug, the loose pile is larger, which matters when you plan where the soil goes and how many truck loads it makes.
Volume per 10 feet of trench
| Width × depth | Cubic feet per 10 ft | Cubic yards per 10 ft |
|---|---|---|
| 1 ft × 2 ft | 20 | 0.74 |
| 1.5 ft × 3 ft | 45 | 1.67 |
| 2 ft × 3 ft | 60 | 2.22 |
| 2 ft × 4 ft | 80 | 2.96 |
| 3 ft × 4 ft | 120 | 4.44 |
Scale by the trench length. A 50 ft trench 3 ft wide and 4 ft deep is 5 × 4.44 = 22.2 cubic yards.
From the hole to a truck
The volume from the calculator is the bank volume, the dirt in place. Soil swells when it is dug.
- Bank volume: 6.667 cubic yards (Example 1)
- With 25 percent swell: 6.667 × 1.25 = 8.33 cubic yards loose
- A truck that carries 10 cubic yards would hold this in one load
The 25 percent is only an example. Your soil, moisture and compaction change it, and your hauler or excavator can give you a figure. When the trench is refilled, the soil settles again, and extra backfill may be needed for the pipe’s bedding, so see the backfill calculator.
Safety and utilities
Trenches can collapse without warning. A cubic yard of soil can weigh well over a ton, and a cave-in can be fatal. In the US, OSHA requires protective systems, such as sloping, shoring or a trench box, for trenches 5 ft deep or more in most soils, with a competent person on site, and it has rules for shallower trenches too. Your local rules may be stricter. For anything more than a shallow hand-dug trench, hire a qualified contractor.
Call 811 before you dig. Buried gas, electric and water lines are common. The call is free, and the utilities mark the lines.
How to measure
- Stake and string the centerline so the length is the true length, including turns.
- Measure the width at the bottom and the top. For sloped sides, use the average.
- Measure depth from the finished grade, and check it at several points along the run.
- For a trench with different depths along its length, split it into sections and add the volumes.
- Subtract the volume of a pipe or a gravel bed from the backfill, not from the dig.
Common mistakes
- Mixing units, such as inches for width and feet for length. Convert first. 18 inches is 1.5 ft.
- Treating the bank volume as the loose volume when you order trucks.
- Forgetting that the trench is wider at the top if the sides slope.
- Using the nominal pipe size as the trench width. The trench must be wide enough for the pipe, the bedding and the person working in it.
- Skipping 811 and the safety rules.
Related calculators
For pricing the dig, see the excavation cost calculator. The French drain gravel calculator sizes the stone that goes in the trench, and the cubic yard calculator handles other shapes.
Frequently asked questions
Is a trench just a box shape?
For this calculator, yes. It multiplies length × width × depth, which gives the volume of a rectangular box. That fits a trench with vertical sides and a flat bottom. A trench with rounded or sloped sides needs a different calculation.
What if the trench has sloped sides for safety?
Then the real volume is larger than the box. A sloped trench is wider at the top than the bottom, so use the average width in the calculator. Sloping, shoring or a trench box is a safety requirement in many cases, so follow OSHA or your local rules and ask a competent person.
Does this tell me how much dirt to remove or how much backfill I need?
It gives the volume of the hole. That is the dirt you dig out, before swell. For backfill, subtract the volume taken up by the pipe, conduit or gravel bed, and add extra if the soil will be compacted in layers. The backfill calculator handles that side.
How much does excavated soil expand when dug out?
Loosened soil takes up more room than it did in the ground, often by 20 to 30 percent, depending on the soil type. Rock and clay can swell more. Use your hauler's figure when you order trucks or dumpsters.
What's a typical trench size for utility lines?
It depends on the line, the local code and the frost depth. Narrow trenches of 1 to 2 ft wide are common for small pipes and cables. Depth is set by the code and the utility, so check with your local utility and call 811 before you dig.
Estimates only. Verify quantities with your supplier before purchasing.