Cut and Fill Calculator
Works out excavation and fill for levelling a site, with the bulking and compaction factors that make the two volumes differ, and tells you whether you will have spoil to remove or fill to import.
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The formula
cut loose = cut area × depth × (1 + bulking) fill loose = fill area × depth ÷ (1 − shrinkage) net = cut loose − fill loose
Soil is not conserved by volume. Dug out, it bulks by a quarter or more; placed and compacted, it shrinks below its loose volume. A site that balances on the drawing — equal cut and fill — usually has spoil left over, because the same earth is bigger coming out than going back in.
What to watch out for
Why cut never equals fill:
- Bulking. Clay and loam expand 20–30% when dug; rock can be 50%. Every lorry load is loose volume.
- Shrinkage. Fill compacted in layers ends up smaller than the loose volume placed — about 10% for granular, more for clay.
- Topsoil is not fill. It is stripped first and either reused on top or sold, never buried under something that has to stay level.
Average depths are the weak point of this calculation. On a sloping site, divide it into a grid, estimate the depth at each node and average those — a single guessed depth over a large area is where estimates go badly wrong.
Frequently Asked Questions
How do I calculate cut and fill?
Multiply each area by its average depth, then inflate the cut by the bulking factor and the fill by the compaction factor. 60 m² cut 0.4 m deep with 25% bulking is 30 m³ of loose spoil; 40 m² filled 0.3 m with 10% shrinkage needs 13.3 m³ loose — leaving about 16.7 m³ to take away.
What is the bulking factor for soil?
20–30% for clay and loam, 10–15% for sand and gravel, 40–50% for broken rock. It is the reason a hole produces more spoil than its own volume.
Can I use the excavated soil as fill?
Subsoil, usually yes, placed in layers and compacted. Topsoil, no — the organic content decomposes and the ground settles for years afterwards.