Start with the volume your project needs, then convert it into the right bags or loose load for the material you have chosen. This avoids the common mistake of treating “one bulk bag” as a fixed amount of coverage.
1. Measure the area
For a rectangle, multiply length by width in metres. Split an L-shaped space into rectangles, calculate them separately and add the areas. Measure the actual space to be filled, leaving out beds or other features that will remain uncovered.
2. Choose the laying depth
Use the depth specified for your project and convert millimetres to metres by dividing by 1,000. For example, 50mm is 0.05m. A decorative border, path and vehicle surface may need different construction, so choose the design before estimating material.
3. Calculate volume
Volume (m³) = length (m) × width (m) × depth (mm) ÷ 1,000.
| Example area | Example depth | Volume |
|---|---|---|
| 4m × 3m | 50mm | 0.60m³ |
| 10m × 1m | 40mm | 0.40m³ |
| 5m × 4m | 50mm | 1.00m³ |
These depths demonstrate the maths; they are not installation specifications. An allowance for uneven ground, cutting boundaries or compaction should come from your actual design and installer.
4. Estimate the gravel weight and bag count
TMG’s gravel calculator uses 1,500kg per m³ to estimate weight automatically. Multiply your volume, including any chosen allowance, by 1,500. For example, 0.60m³ gives an estimated 900kg, or 990kg with a 10% allowance. Actual weights vary by material and condition.
Estimated pack count = round up [estimated weight ÷ minimum pack weight]. Choose Bulk Bag (750kg), Loose Load (750kg), Mini Bulk Bag (250kg) or Mini Bag (20kg) in the calculator. These are the minimum weights advertised on our gravel product pages. Loose loads are tipped without a bag. Ask TMG to check the quantity for your product and project.
Match the calculation to a TMG product
20mm Grey Gravel, 20mm Golden Gravel and 20mm Pea Gravel offer different shapes and appearances. Their product pages list mini bags, mini bulk bags, bulk bags and tipped loose formats. The current advertised minimum weights are 20kg, 250kg and 750kg for the respective bag sizes; check your selected format and supplied weight with TMG when converting a calculated volume into an order.
5. Plan where the material will go
A tipped load needs an agreed place for loose material. Bagged material needs suitable access and a placement plan. Share the postcode, entrance details and chosen format before booking a delivery for a restricted site.
Open the project quantity tools · Read delivery and collection information · Ask TMG to check your quantity