Fill Dirt Calculator

About the Fill Dirt Calculator

Raising the level of the ground, whether to fix a low spot that floods, level a sloping yard, build a pad for a shed or bring a garden up to a new patio, takes more fill dirt than the simple volume suggests. Dirt delivered by truck is loose and full of air. When it is spread and compacted, as it must be to stop it settling later, it shrinks. If you order only the finished volume, you run short.

This fill dirt calculator starts from the height you want to raise the ground after compaction. It works out the compacted volume, then the loose volume you need to order to allow for shrinkage, the number of dump-truck loads and how many lifts to place and compact.

How to Use the Fill Dirt Calculator

Enter the length and width of the area in feet.

Enter how much to raise the ground, in inches, as the finished compacted height.

Enter the shrinkage when compacted, typically 10 to 25%, and the dump truck size.

The Formulas

  compacted yd³  = length × width × raise ÷ 324
  loose yd³      = compacted yd³ ÷ (1 − shrinkage)
  loads          = ⌈loose yd³ ÷ truck size⌉
  lifts          = ⌈raise ÷ 6 in⌉

Step-by-Step Example

Raising a 30 × 20 ft area by 12 inches with 20% shrinkage.

  compacted  30 × 20 × 12 ÷ 324 = 22.22 yd³
  loose      22.22 ÷ 0.8 = 27.78 yd³ (about 33 tons)
  loads      ⌈27.78 ÷ 10⌉ = 3 loads
  lifts      ⌈12 ÷ 6⌉ = 2 lifts

Why Divide Rather Than Multiply?

Shrinkage is the share of loose volume that disappears when compacted. With 20% shrinkage, each loose yard becomes 0.8 compacted yards. To finish with 22.22 compacted yards you therefore need 22.22 ÷ 0.8 = 27.78 loose yards, which is 25% more than the compacted volume, not 20%. Multiplying by 1.2 instead would leave you about a yard and a half short on this job. The difference grows with higher shrinkage.

How Much Does Fill Shrink?

Shrinkage depends on the soil and its moisture. Sandy and gravelly fill drains well and compacts quickly, typically shrinking 10 to 15%. Common loamy fill shrinks about 15 to 20%. Clay can shrink 20 to 30% from a loose truckload, but it is hard to compact when wet and cracks when dry. If you are unsure, use 20% and keep a small pile in reserve. Excavation contractors sometimes measure shrinkage by weighing a known volume before and after compaction.

Placing Fill in Lifts

Fill must be compacted in layers, called lifts. A plate compactor firms about 4 to 6 inches at a time; a vibrating roller can handle more. Spread a layer about 8 inches loose, compact it to about 6 inches, then add the next. Dirt that is slightly moist compacts best: it should hold together when squeezed, without water running out. A single thick dump of fill spread with a bucket will look level for a while and then settle unevenly over months or years.

Building on Fill

Ordinary fill dirt is fine under lawns and gardens. Anything structural is different. Slabs, footings, retaining walls and driveways need fill placed as engineered fill: a suitable soil, placed in controlled lifts and tested to reach a specified density, often 95% of its maximum. Building departments may require compaction test reports. Without them, buildings on fill can crack as the ground settles beneath them.

Drainage and Grading

When raising ground near a house, slope the finished surface away from the foundation, about 6 inches over the first 10 feet, so rainwater runs away from the walls. Do not pile fill against siding or above the foundation's weep holes and damp-proof course. Raising the ground on your lot can also change where water flows onto neighbours' property, and some areas need a permit for fill.

Finishing with Topsoil

Fill dirt is poor at growing plants. For a lawn or garden, stop the fill 4 to 6 inches below the finished grade and top it with screened topsoil. Calculate the fill raise as the total raise minus the topsoil depth, and order the topsoil separately.

Checking Your Grade

To find how much the ground needs raising, set stakes at the corners of the area and run a level string between them at the target height. Measure from the string down to the ground at several points and average the readings. That average is the raise to enter. On sloping sites, splitting the area into strips and calculating each separately gives a more accurate total.

Choosing Good Fill

Good fill dirt is free of topsoil, roots, wood, rubbish and large rocks, all of which leave voids or rot and cause settling. Sandy or gravelly subsoil compacts most predictably. Ask the supplier whether the fill is screened and where it came from, and inspect the first load before accepting more, especially if it is free fill from a building site.

Understanding Your Result

The headline gives the loose fill dirt to order.

The compaction line shows the compacted volume and the shrinkage allowance.

The truckloads line gives the number of loads.

The placing line gives the number of lifts to compact.

When Should You Use This Calculator?

Use it when raising a low area, levelling a yard or building a pad.

Use it to check that a contractor's quote allows for compaction.

Use it to plan how many days of spreading and compacting a job needs.

Common Mistakes

Ordering the finished volume. Allow for shrinkage.

Multiplying instead of dividing. 20% shrinkage needs 25% extra.

Dumping fill in one layer. Compact it in lifts.

Building on untested fill. Structures need engineered fill.