Calculate soil volume in litres and cubic metres, then convert the result into the number of bags to buy.
Buying raised-bed soil by guesswork is expensive. Enter the internal length, width and fill depth of the bed, then choose the bag size sold by your supplier.
Volume is length × width × depth. The result is converted from cubic metres to litres, then rounded up to whole bags so you do not come up short during filling.
A bed with internal dimensions of 2 m × 1 m filled to 0.30 m needs 0.60 m³, or about 600 litres, before any allowance for settlement. If the chosen product is sold in 40 L bags, the simple volume works out to 15 whole bags.
A bed that is 2 m long, 1 m wide and filled to 0.30 m needs 0.60 m³, or about 600 litres. With 40-litre bags, the mathematical minimum is 15 bags before any allowance for settlement or an uneven base.
Measure the internal dimensions of the space that will actually be filled. Thick timber, masonry edges and tapered containers can make exterior measurements overstate the soil volume.
Fresh mixes often settle after watering and over the first season. If the bed is deep, consider whether the full depth really needs premium growing mix or whether an appropriate lower layer is part of your design. The calculator reports volume; it does not prescribe a soil recipe.
For small jobs, rounding up to whole bags is usually enough. Larger or irregular beds often benefit from a small extra allowance for settlement and measurement error.
This version is for rectangular beds. Circular or irregular shapes need a different area formula before multiplying by depth.