Aggregate Calculator — Tonnes from Area & Depth
Work out how many tonnes of aggregate you need from the area, finished depth, ordering allowance and an editable bulk-density figure. Metric-first, instant and no sign-up.
Enter your measurements
How this aggregate calculator works
The calculator first turns your area and layer depth into a geometric volume in cubic metres. It then applies the ordering allowance you choose and converts that adjusted volume to tonnes using the bulk density entered.
Order volume = volume × (1 + allowance %)
Estimated tonnes = order volume × bulk density (t/m³)
The default density is a planning value only. Aggregate density varies with material, grading, moisture, source and whether a supplier quotes loose or compacted data. Replace the default with the figure for the actual product whenever your supplier or specification provides one.
Worked example: 50 m² at 75 mm
Which depth should I enter?
Enter the finished layer depth relevant to the job you are estimating. If a specification requires a compacted layer, use that specified compacted thickness for the geometry and then use appropriate product/supplier information when converting the volume to an order quantity. Do not silently treat loose delivered depth, compacted depth and excavation depth as interchangeable.
If you are estimating MOT Type 1 specifically, use the dedicated MOT Type 1 Calculator. For excavated spoil rather than incoming aggregate, use the Excavation Volume Calculator.
Why bulk density changes the tonnage
Different aggregates weigh differently
Crushed stone, gravel, sand and recycled products do not all have the same mass per cubic metre.
Moisture and grading matter
Bulk density can change with void space, particle grading and moisture condition, so a single universal conversion is misleading.
Supplier data beats a generic default
Use the actual product density or supplier conversion where available, then round to the supplier’s real delivery or bag unit.
For more detail on the assumption, see the Aggregate Bulk Density Guide. For the wider buying workflow, use the Aggregate Ordering Guide.
How much aggregate do I need?
For a simple rectangular area, you need four pieces of information: area, finished depth, an allowance and a density. Measure the real area, convert the required depth to metres, calculate cubic metres, then convert that volume to tonnes. For irregular areas, split the job into measurable sections and add the volumes before applying the final ordering logic.
Common aggregate estimating mistakes
- Using millimetres as though they were metres when calculating volume.
- Applying a generic density to every aggregate without checking the selected product.
- Confusing compacted finished depth with loose delivered depth.
- Adding an allowance twice — once to volume and again to the supplier quantity.
- Ordering an exact calculated mass without checking the supplier’s minimum load, bag size or delivery increments.
Before you order aggregate
Confirm the product type, layer specification and density/conversion with the supplier. Then compare the calculator’s estimated tonnes with the supplier’s sales unit. HMRC’s current Aggregates Levy guidance also reflects the commercial convention that construction aggregate such as rock, gravel and sand is commonly accounted for by tonnage, but that does not create one universal tonnes-per-cubic-metre conversion for every product.
Planning estimate only. This tool estimates quantity; it does not verify structural design, drainage performance, compaction requirements, product suitability or compliance with a project specification.
Frequently asked questions
How do I calculate tonnes of aggregate from square metres?
Multiply the area in square metres by the depth in metres to get cubic metres, apply any ordering allowance, then multiply by the relevant bulk density in tonnes per cubic metre.
How many tonnes is 1 cubic metre of aggregate?
There is no single correct figure for every aggregate. The answer depends on material, grading, moisture and how the density is defined. Use the supplier or product density where possible.
What bulk density should I use?
Use a value supplied for the actual aggregate whenever available. The calculator’s pre-filled density is only a starting assumption and is deliberately editable.
Should I add an allowance when ordering aggregate?
An allowance can help cover measurement variation and site losses, but the appropriate percentage depends on the job. Keep it visible and editable rather than hiding it inside the density.
Does this calculator work for MOT Type 1?
It can perform the basic area-depth-density conversion, but the dedicated MOT Type 1 Calculator gives a clearer workflow for that material and keeps its assumptions explicit.
Should I round the answer up?
Round to the supplier’s real sales unit or delivery increment after checking the product data. The calculator shows an estimated mass rather than pretending every merchant sells identical quantities.
Related aggregate tools
Need bags rather than tonnes? Use the Aggregate Bag Calculator. Planning excavation waste instead? Use the Skip Size Calculator. You can also return to the full Groundworks calculator hub.