How to use the trench and excavation volume calculator
- Choose the shape: a trench or pit with straight sides, a trench with sloped sides, or a round hole.
- Choose a unit and enter the length, width and depth, or the diameter and depth with the number of holes.
- For sloped sides, enter the side slope as horizontal distance per 1 unit of depth.
- Enter the soil swell and your truck capacity to see the loose volume and the number of trips.
Formula
Straight sides: volume = length x width x depth
Sloped sides: volume = (bottom width + slope x depth) x depth x length
Round hole: volume = pi x (diameter / 2)^2 x depth x number of holes
1 cubic yard = 27 cubic feet; loose volume = volume x (1 + swell)
In a trench with sloped sides, each side leans out by the slope times the depth, so the top is wider than the bottom by twice that amount.
Worked example
A trench 50 feet long, 2 feet wide and 3 feet deep holds 300 cubic feet, which is 11.11 cubic yards. With 25% swell the loose soil is 13.89 cubic yards, or 2 truck loads of 10 cubic yards.
If the same trench has sloped sides with a slope of 0.5, the volume is (2 + 0.5 x 3) x 3 x 50 = 525 cubic feet, or 19.44 cubic yards, and the top is 5 feet wide. Four round holes 2 feet across and 3 feet deep hold 37.7 cubic feet.
Swell and hauling
Soil takes more space once it is dug, because the particles are loosened and air gets between them. The amount depends on the soil type, so the 25 percent here is only an example. The loose volume is what you need for trucks and for stockpiles. After the work is done, backfilled soil will compact, so you may need more or less than you took out.
Safety and rules
Call your local utility locator service before you dig so that buried lines are marked. Deep trenches can collapse, and workplace safety rules set when shoring, sloping or benching is needed. Slopes and depths in this tool are arithmetic only. They do not tell you what is safe for your site.
Related tools
To order concrete for a footing use the concrete calculator, and for post holes the post hole concrete calculator. Material for backfill or a base layer can be found with the mulch and gravel calculator, and other shapes with the volume calculator.
Assumptions and limits
- Walls are straight, or sloped at one constant slope, and the bottom is flat.
- Swell and truck capacity are example values. Your soil and trucks will differ.
- Rock, water, existing structures and over-excavation for working room are not modeled.
- Volumes are shown to two decimals and trips are rounded up to a whole truck.
Frequently asked questions
How many cubic yards is a trench?
Multiply length, width and depth in feet to get cubic feet, then divide by 27. A trench 50 by 2 by 3 feet is about 11.1 cubic yards.
What is swell in excavation?
It is the increase in volume when soil is dug up and loosened, shown as a percent of the volume in the ground.
How do I calculate a trench with sloped sides?
Use a trapezoid for the cross-section: the average width times the depth, then multiply by the length.
How many truckloads of dirt do I need to haul?
Divide the loose volume by the truck's capacity and round up. The tool shows both numbers.