Fill Dirt Calculator
Works out fill dirt for raising ground, backfilling or levelling. Enter the finished depth you want — fill is compacted in layers, so the loose volume ordered comes out higher, and that is already allowed for.
Includes the waste allowance — this is the figure to order.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
volume = length × width × depth × compaction × (1 + waste) weight = volume × bulk density
The geometry is trivial; the bulk density is where the answer actually comes from. Fill dirt runs about 1400 kg per cubic metre loose, so a cubic metre weighs roughly 1.40 tonnes. Suppliers quote one or the other, which is why both are given.
What to watch out for
Fill dirt is structural, which makes it a different material from topsoil in every way that matters:
- No organic content, deliberately. Organic matter rots and the ground subsides years later. Fill is subsoil for exactly that reason.
- It must be compacted in layers. 150–200 mm at a time. Tipped in one heap and left, it settles unevenly for years.
- Nothing grows in it. Cap with 100–150 mm of topsoil if the surface is going to be planted or seeded.
Fill is often free or near-free — sites excavating a basement pay to get rid of it. The cost is usually the haulage, not the material.
Frequently Asked Questions
What is the difference between fill dirt and topsoil?
Fill dirt is subsoil with the organic matter removed, used to build ground up. Topsoil is the living upper layer that things grow in. Using topsoil as structural fill causes subsidence as the organic content decomposes.
How much fill dirt do I need?
Length × width × depth, plus about 20% for compaction. A 6 × 4 m area raised 300 mm needs 7.2 m³ finished, which is closer to 9.5 m³ of loose material delivered.
Does fill dirt need to be compacted?
Yes, in layers of 150–200 mm. Uncompacted fill keeps settling for years, which is how patios develop dips and retaining walls start to lean.