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Excavation Calculator

Updated How we build and test

Enter the size of the hole to see how many cubic yards of soil come out, how much room that soil takes once it is dug and how many truckloads it is.

Horizontal : vertical. Sloped sides make the top of the hole wider.

%

Dug soil takes up more room than it did in the ground. 20 to 30% is typical for common earth.

yd³

Soil to excavate

Enter the length, width and depth of the excavation.

How to use the excavation calculator

  1. Enter the length and width at the bottom of the excavation and its depth. For a trench, the length is the run and the width is the trench width.
  2. Choose vertical sides for shallow digs and trenches in a trench box. Choose a slope if the sides will be cut back.
  3. Set the swell for your soil and the size of the truck to get the loads to haul.

Formulas

Vertical sides: volume = length × width × depth
Sloped sides: top length = length + 2 × slope × depth (same for width)
Volume = depth ÷ 6 × (bottom area + top area + 4 × middle area)
Cubic yards = cubic feet ÷ 27
Loose volume = cubic yards × (1 + swell % ÷ 100)
Truckloads = loose volume ÷ truck capacity, rounded up

The sloped-side figure uses the prismoidal formula, which is exact for a hole with a flat rectangular bottom and evenly sloped sides. The middle area is the cross-section halfway down. Volume in the ground is called bank volume; contractors and haulers charge on the loose volume, which is larger.

Worked example: a 20 × 10 ft pit, 4 ft deep

  1. Vertical sides: 20 × 10 × 4 = 800 ft³, and 800 ÷ 27 = 29.6 yd³.
  2. Loose volume at 25% swell: 29.6 × 1.25 = 37.0 yd³.
  3. Truckloads at 10 yd³: 37.0 ÷ 10 = 3.7, so 4 loads.
  4. With 1 : 1 sloped sides the top becomes 28 × 18 ft and the middle 24 × 14 ft: 4 ÷ 6 × (200 + 504 + 4 × 336) = 1,365 ft³, or 50.6 yd³ in the ground.

Questions

How do I calculate cubic yards of excavation?

Multiply length by width by depth in feet and divide by 27. A hole 20 ft long, 10 ft wide and 4 ft deep is 800 ft³, or 29.6 yd³.

What is soil swell?

Soil loosens when it is dug and takes up more space than it did in the ground. Sand and gravel swell around 10 to 15%, common earth 20 to 30% and clay 30% or more, so a 30 yd³ hole can fill 37 yd³ or more of truck space.

When do the sides of an excavation need to be sloped?

OSHA requires a protective system such as sloping, benching, shoring or a trench box for excavations 5 ft or deeper, unless the excavation is entirely in stable rock. The maximum allowable slopes are 3/4 : 1 for Type A soil, 1 : 1 for Type B and 1 1/2 : 1 for Type C. A competent person must classify the soil on site; this calculator only works out the volume.

Sources

  1. 29 CFR 1926 Subpart P, Appendix B: Sloping and Benching, Occupational Safety and Health Administration. Used for: maximum allowable slopes by soil type.

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