How Many Cubic Yards of Dirt Will I Dig?

Working out cubic yards of dirt for an excavation is one multiplication and one division. Working out what leaves the site is a different number entirely, and the gap between them is where excavation quotes stop matching the arithmetic people did at the kitchen table.

The hole

Length × width × depth in feet, divided by 27.

A 30 × 20 foot hole, 3 feet deep: 1,800 cubic feet ÷ 27 = 66.7 cubic yards.

The 27 comes from a cubic yard being three feet on every side. It is the same divisor used when calculating concrete in cubic yards, and forgetting it is the most common single error in material estimating.

That figure is the size of the hole. It is not what you are hauling away.

Soil swells when you dig it

Soil in undisturbed ground has been compressed by its own weight and by geological time. Dig it out and it fluffs — the grains no longer nest, air fills the voids, and the same material occupies noticeably more space.

The industry has three names for the three states:

• Bank cubic yards (BCY) — volume in place. The size of the hole, and what you calculate from dimensions.
• Loose cubic yards (LCY) — volume after excavation. What fills the truck, and what haul-off is priced on.
• Compacted cubic yards (CCY) — volume after being placed and compacted again, which is less than bank.

Typical swell from bank to loose:

Material	Swell
Sand and gravel	12%
Topsoil	25%
Common earth	25%
Clay	30%
Blasted rock	50%

So that 66.7-yard hole in clay produces about 87 loose cubic yards to move — seven tandem loads instead of five and a bit.

That gap is where "the excavation quote came in higher than my math" almost always lives, and it is not padding.

The excavation calculator applies the swell factor for your soil type and converts the result into truckloads at whatever capacity your hauler runs.

Weight is usually the real constraint

A tandem dump truck rated for 14 cubic yards will rarely leave a site with 14 cubic yards of clay in it, because it will hit its legal axle weight first.

Rough in-place weights per cubic yard: topsoil 2,400 lb, common earth 2,800, clay 3,000, sand and gravel 3,200, rock 4,000. Wet material adds 20 to 30 percent on top of that.

A 14-yard box of wet clay is well over 20 tons of payload, which no tandem is legal to carry. Which is why haul-off is frequently quoted per ton rather than per load, and why the tonnage matters as much as the yardage. The cubic yards to tons converter handles that conversion for the material going back in, which follows the same density logic.

If you are moving material yourself, the trailer load calculator is worth a look first — a single cubic yard of soil is close to the payload limit of many utility trailers.

Backfill is dirt that never leaves

Not everything you dig gets hauled. Foundation excavation typically returns a large share of the spoil once the walls are up, and utility trenches are usually backfilled with their own spoil apart from a stone bed.

Paying to haul soil off site and then paying again to bring soil back is a distressingly common way to spend money, so work out the backfill share before anyone books a truck.

Two cautions. Strip and stockpile topsoil separately — it is the most valuable material on the site and mixing it into subsoil backfill wastes it entirely. And spoil is not always suitable backfill: expansive clays and organic material do not compact usefully against a foundation, and using them there loads a wall in ways nobody designed for.

Call 811 first

Free, legally required in every state, a few business days' notice. Locators come out and mark public utilities in the dig area.

It does not cover private lines — the run to a detached garage, an irrigation main, a propane line, an invisible fence — so those are yours to know about.

The asymmetry is extreme. The call costs nothing. A struck gas line is life-threatening and a struck fibre trunk can produce a five-figure bill within minutes. There is no version of this where skipping it is the right call.

Trench depth and the five-foot line

Once a trench is roughly five feet deep, OSHA requires a protective system — sloping the walls back, benching them, or using a trench box.

Soil weighs around 3,000 pounds per cubic yard. A collapse gives no warning, and someone buried to the chest cannot self-extract and often cannot breathe. Trench collapses kill people in the US every year, almost always in excavations that "were only going to be open for an hour."

Depth is not the only factor — soil type, adjacent loads, vibration and water all matter — but five feet is where the rules become explicit.

What the rectangle misses

A rectangular calculation is exact for a rectangular hole and optimistic for a real one.

Over-dig and working room. A foundation hole is dug larger than the foundation so people can work outside the forms. Add it to your dimensions.

Sloped or benched walls add substantial volume on a deep excavation, and a box calculation does not see any of it.

Rock, water and unsuitable material are the three things that turn an excavation quote into a change order, and none of them are visible until someone digs.

For what goes back into the ground afterwards, the gravel calculator covers stone by volume and weight, and the french drain calculator sizes the trench that keeps water away from whatever you just built.

For trenching safety requirements, OSHA publishes guidance that is short, plain and worth ten minutes before any deep dig.