Plot No. 66 · Home & Garden
Raised Bed Soil Calculator
Work out how much soil a raised bed needs to fill. It multiplies the bed length by width by fill height to get the volume in cubic metres, then converts that to litres and to the number of standard 50 litre bags of compost or topsoil to buy.
Bag counts are rounded up to whole bags. Fresh compost settles, so fill near the top and plan to top up the following spring.
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How the raised bed soil volume is worked out
The calculator multiplies the bed length by width by the fill height to get the volume in cubic metres, converting the height from centimetres to metres. That is the space inside the frame you need to fill with soil or compost.
It then multiplies cubic metres by 1,000 to give litres, and divides litres by 50 and rounds up to give the number of standard 50 litre bags. Bagged compost and topsoil are sold in 50 litre sacks, so the bag count is what you actually order.
How to use the raised bed soil calculator
- Enter the bed length and width in metres.
- Enter the fill height in centimetres, for example 30 for a deep bed.
- Read off the volume in cubic metres, the litres of soil and the number of 50 litre bags to buy.
Worked examples
Standard timber raised bed
Inputs: 2 m by 1 m bed, 30 cm fill height
Result: 0.6 cubic metres, which is 600 litres of soil, or exactly twelve 50 litre bags.
Shallow salad bed
Inputs: 2 m by 1 m bed filled only 15 cm deep
Result: 0.3 cubic metres, 300 litres, six 50 litre bags, enough for shallow-rooted leaves and herbs.
Limitations and common mistakes
Edge cases and limitations
- Fresh compost settles by 10 to 20 percent in the first season, so the level will drop and need topping up.
- It gives the total volume only. Split that across your chosen mix, such as topsoil and compost, when ordering.
- Bags are rounded up, so use the litres figure when buying loose soil by volume.
Common mistakes
- Filling a deep bed entirely with pure compost, which slumps and dries out, instead of blending in topsoil.
- Confusing litres with bags and ordering far too few, since each bag is 50 litres not one litre.
Frequently asked questions
How much soil does a raised bed need?
Multiply length by width by fill height. A 2 m by 1 m bed filled 30 cm deep is 0.6 cubic metres, which is 600 litres, or twelve 50 litre bags of soil or compost.
What soil mix works in a raised bed?
A common blend is roughly 60 percent quality topsoil and 40 percent garden compost. This calculator gives the total volume to fill, so split that figure across your chosen mix when you place the order.
Why does the soil level drop after a few weeks?
Fresh compost settles and breaks down, so the level can fall by 10 to 20 percent in the first season. Fill close to the top at the start and top up with compost the following spring rather than over-ordering now.
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