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Gravel calculator in tonnes and bulk bags
Convert a measured material area and depth into cubic metres, tonnes and 850 kg or 1 tonne bulk bags using your supplier’s stated density.
Your result
Your plan starts
with a few details.
Enter your project measurements and product details, then calculate to see an estimated take-off.
How it works
Choose a material to load its cited conversion factor, then enter the measured area, matching volume condition, depth and selected comparison bag mass. The density field remains editable for an exact supplier quote.
Gravel: 1.75 t/m³. Indicative loose-laid 10–20 mm gravel/shingle conversion; confirm the exact supplier product.
MOT Type 1: 2 t/m³. Indicative compacted Type 1 conversion. Do not apply this to a loose delivery volume.
Sharp sand: 1.6 t/m³. Rospower indicative sharp/grit sand conversion; moisture affects density. Confirm your exact product and volume condition.
Topsoil: 1.5 t/m³. Mainland Aggregates screened topsoil, approximate product-specific density. Its own bag is 800 kg; the selectable 850/1000 kg options are comparison masses, not a claim about that product bag.
Formula
Work out volume
Volume (m³) = area (m²) × depth (mm) ÷ 1,000This is the geometric volume at the entered depth, before compaction, settlement or site variation.
Convert to mass and bags
Tonnes = volume × entered density (t/m³) Bulk bags = ceil(tonnes × 1,000 ÷ bag mass (kg))Whole-bag rounding assumes the selected bag contains the stated mass. Confirm product mass and delivery units with the supplier.
Worked example
For 20 m² at 50 mm deep, volume is 20 × 50 ÷ 1,000 = 1 m³. If the chosen product sheet states 1.7 t/m³, the estimated mass is 1.7 t, or ceil(1,700 ÷ 850) = 2 bags of 850 kg. The density here is an example input only, not a default for any listed material.
Assumptions and limits
Bulk density changes with grading, moisture, packing and compaction. A volume-to-tonnes conversion should use the supplier’s data for the exact product. The UK government materials statistics provide market indices and selected industry data, not a density table for every aggregate product.
The estimate does not include excavation swell, compaction loss, contamination, delivery limits or minimum order quantities. Check whether your supplier sells by loose cubic metre, weight or nominal bulk bag.
Frequently asked questions
How many tonnes of gravel do I need?
Calculate the geometric volume, then multiply it by the density printed for your chosen aggregate. Enter both values to see tonnes and bulk bags.
Can I use the same density for sand and gravel?
Use the value for the exact material and condition you are buying. Different products and moisture levels can have different bulk densities.
Is a bulk bag always one tonne?
No. Choose the stated bag mass you will buy. An 850 kg bag contains less material than a one-tonne bag, so the same tonnage can require more bags.
Should I use loose or compacted volume?
Match the volume condition to the selected density source. A compacted sub-base depth needs a compacted conversion basis; a loose gravel or topsoil layer needs its own appropriate density.
Sources
Specs as of: