GardenCalcs.uk
Soil Volume Calculator
Calculate soil needed for raised beds, planters, and containers of various shapes.
Choose the shape of your bed or container
Longest side of the bed, measured along the ground
Shortest side of the bed, measured along the ground
Fill depth of soil. Allow 150-300 mm (0.15-0.30 m) for raised veg beds, more for deep-rooted crops
Number of identical beds or containers with these same dimensions
Price of one small bag. Used to estimate total cost from the bag count; leave 0 to skip
Litres in each small bag of soil or compost (commonly 40, 50 or 60 L)
Volume of one bulk (tonne) bag. UK 850 kg bags hold about 0.6-0.7 m³; set to your supplier’s figure
Extra volume to order so the bed stays full after settling (10-15% for fresh topsoil)
How We Calculate This
Volume is calculated from your container dimensions using standard geometry for each shape: length × width × depth for a rectangle, π × radius² × depth for a round bed, and ½ × base × height × depth for a triangular prism.
An L-shaped bed is treated as its overall bounding rectangle with a rectangular corner notch removed, so the result is always less than the full rectangle — measure the overall length and width, then the size of the cut-out corner.
A compaction factor (default 10%) is added to allow for settlement, then the figure is converted to litres (1 m³ = 1000 litres), small bags, bulk bags (default 0.7 m³ each) and an approximate weight at 1.4 t/m³ for screened topsoil.
Working figures for this are collected in our Soil Volumes reference table.
Frequently Asked Questions
Screened topsoil weighs roughly 1.4-1.6 tonnes per cubic metre once settled (BS 3882 material is typically 1.2-1.6 t/m³ depending on moisture). Compost is much lighter at around 0.4-0.6 t/m³. This calculator estimates weight at 1.4 t/m³, a sensible central figure for screened topsoil.
Yes. Fresh topsoil and compost in raised beds settle by 10-15% over the first season as organic matter breaks down and the soil consolidates. The compaction factor in advanced options adds this allowance, so fill beds slightly proud and top up after the first winter.
A standard UK bulk bag (also called a tonne bag or dumpy bag) holds roughly 0.6-0.7 m³ of soil and weighs around 850 kg-1 tonne, so this calculator uses 0.7 m³ by default. They work out cheaper per litre than small bags for larger projects and are usually delivered by lorry with a crane or grab. Check your supplier’s stated volume, as it varies.
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Last updated: March 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.