How to Calculate Aggregate Tonnes for a Job
Quick answer
Aggregate volume is area × layer depth in metres. Tonnes = volume × the density appropriate to that volume basis. For a finished compacted layer, use a supported compacted-density assumption and confirm the ordering basis with the supplier.
Measure each layer separately
Split irregular areas into rectangles or triangles, calculate each area, and add them together. Multiply by the specified finished thickness for each material layer. Keep millimetres and metres consistent: a 150 mm layer is 0.15 m.
- —Separate basecourse, subbase and drainage material.
- —Use the measured or designed shape rather than a single maximum width.
- —Allow for level changes or undercut as separate measured work.
Convert volume to tonnes using a stated assumption
There is no single density that fits every aggregate or moisture condition. Use project information, supplier advice or measured records for the material. A product name alone is not a reliable conversion factor.
Formulas
Area of a rectangle = length × width
Layer volume = area × depth in metres
Estimated tonnes = layer volume × density in tonnes per m³
Order allowance = estimated tonnes × allowance percentage ÷ 100
Worked example: an access area
The density and allowance are examples, not a recommendation for a particular aggregate. Replace them with inputs appropriate to the job.
Worked example
Area 25 m × 8 m = 200 m².
Finished layer thickness 150 mm = 0.15 m.
Volume = 200 × 0.15 = 30 m³.
At an illustrative compacted density of 2.1 t/m³: 30 × 2.1 = 63 tonnes.
A separately chosen 5% ordering allowance adds 3.15 tonnes: total 66.15 tonnes.
Check what the supplier will deliver
- —Confirm whether the quote is per tonne, loose cubic metre or load.
- —Check whether moisture, handling or compaction changes the comparison with your takeoff.
- —Plan access and staged deliveries to avoid handling material twice.
- —Reconcile dockets with installed quantities and remaining stock before ordering the final loads.
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