Inside dimensions make the difference.
Geometry = area × depth · Order volume = geometry × loose-volume multiplier × (1 + waste ÷ 100)
Measure inside the frame
The outer footprint includes boards or blocks that do not hold soil. Measure the internal length and width, then measure the depth from the current fill surface to the intended final level. The full height of the frame is not necessarily the fill depth.
Count identical beds; split different ones
The identical-area count multiplies the measured volume. Use it when all beds have the same inside dimensions and remaining fill depth. For different beds, calculate each one and add separate entries to the shopping list. Account for large solid inserts by measuring the remaining fill space rather than counting occupied volume.
A worked raised-bed example
Two beds, each 4 ft × 8 ft internally with 12 in left to fill, need 64 ft³ in total. At 2 ft³ per bag, the unadjusted order is 32 bags. At 40 litres per bag, the same geometric quantity is about 1,812.28 litres and needs 46 bags.
Record each different bed
Identical-bed count is a shortcut only when inside dimensions and remaining fill depth match. For mixed beds, save an estimate for each size with a label such as “short bed” or “round herb bed”. The shared list now follows you between calculators and remains after reload.
Leave already occupied space out of the measurement
If a solid insert or existing material occupies some of the bed, measure the actual remaining fill space. Multiplying the outside length by the full frame height would count both the frame and the occupied volume. This tool does not automatically subtract arbitrary objects.
Compare fills using one quantity basis
The tool estimates total growing-medium space, not a recipe. If you have chosen multiple components, calculate each component’s share separately using compatible volume units and record the chosen proportions yourself. It does not decide that a particular mix is suitable.
Before you place an order
Check dimensions, bag yield and the price basis. Whole bags round up; bulk orders may have minimum quantities or delivery charges that this calculator does not include. All adjustments are your inputs. Read our method, unit definitions and limits.
Useful questions
Does the calculator choose a soil blend?
No. It calculates the total space to fill. Choose a growing medium suitable for your plants and bed; this tool does not prescribe a compost/topsoil ratio.
Can I calculate a round raised bed?
Yes. Select circle and enter the inside diameter, or switch to radius. Use the remaining fill depth, not automatically the frame height.