Free raised bed soil calculator. Enter bed length, width and soil depth to find the soil volume in litres and the 40 litre bags you need.
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Enter bed length, width and soil depth. This raised bed soil calculator multiplies them to find the soil volume in litres, then divides by 40 to find the 40 litre bags you need. A 2 metre by 1 metre bed at 30 centimetres deep needs 600 litres, which is 15 bags. Measure the internal dimensions of the bed, not the outside of the frame.
Soil volume is length times width times depth, all in the same units. In metres, a 2 metre by 1 metre bed at 0.3 metres deep holds 2 times 1 times 0.3, which is 0.6 cubic metres, or 600 litres, since one cubic metre holds 1000 litres. This calculator uses length in metres times width in metres times depth in centimetres times 10, which gives the same litres figure directly. Divide litres by 40 to get 40 litre bags.
Competitor guides in feet use a four by eight foot bed as their standard example. At 12 inches deep it needs 32 cubic feet, which is about 1.2 cubic yards, or 22 bags of 1.5 cubic foot soil, or 16 bags of 2 cubic foot soil. At 6 inches deep it needs half that: 16 cubic feet. The cubic yards figure is cubic feet divided by 27, because one cubic yard holds 27 cubic feet.
Most vegetables and herbs grow well in 25 to 30 centimetres, about 10 to 12 inches, of soil. Root crops like carrots and parsnips need 30 to 45 centimetres. Salad leaves and herbs manage in 15 to 20 centimetres. Deeper beds hold moisture better and buffer temperature swings, but every extra centimetre of depth adds litres to buy, so match depth to what you actually grow.
A popular raised bed soil mix recipe is 60 percent topsoil, 30 percent compost and 10 percent perlite or coarse sand. Topsoil gives structure and minerals, compost adds nutrients and microbes, and perlite opens the mix so water drains freely. For a 600 litre bed that means 360 litres of topsoil, 180 litres of compost and 60 litres of perlite. Avoid filling a bed with garden soil alone, which compacts and drains poorly, and never fill it with pure compost, which shrinks and holds too much water.
Measure the inside of the bed, not the outside of the frame. A thick timber frame can steal several centimetres from each side, and on a deep bed that difference changes the litres figure by a whole bag or more. If you are topping up an existing bed rather than filling an empty one, measure only the gap you need to fill, not the full height of the bed.
Fresh soil settles 10 to 15 percent after the first waterings, as air pockets collapse and organic matter breaks down. Fill slightly above your target depth, or buy one extra bag and plan a top up after a few weeks. Beds sink a little each season, so an annual spring top up with compost is normal maintenance, not a sign that you measured wrong.
For beds deeper than 40 centimetres, competitor guides suggest logs or branches at the bottom as hugelkultur filler. Plants do not need soil that deep, and filler saves a large share of the soil bill while improving drainage. Put 15 to 20 centimetres of coarse woody material at the bottom, cover it with a layer of leaves or straw, then fill the top 30 centimetres with your soil mix.
Bagged soil suits small beds: no delivery minimum and easy handling. Bulk delivery by the cubic yard is usually cheaper once you need about a cubic yard or more, but check the delivery minimum and make sure a truck can reach your garden. As a rough guide, bulk topsoil often costs far less per litre than bagged soil, while bags win on convenience for a single small bed.
Multiply internal length by width by depth. A 2 metre by 1 metre bed at 30 centimetres deep needs 600 litres, which is 15 bags of 40 litres.
A four by eight foot bed at 12 inches deep needs 32 cubic feet: about 22 bags of 1.5 cubic foot soil or 16 bags of 2 cubic foot soil.
Most vegetables need 25 to 30 centimetres. Root crops need 30 to 45 centimetres, while salad leaves and herbs manage in 15 to 20 centimetres.
A common recipe is 60 percent topsoil, 30 percent compost and 10 percent perlite or coarse sand. It holds moisture and nutrients while draining freely.
Yes. Fresh soil settles 10 to 15 percent after watering, so fill slightly high or buy one extra bag for a top up after a few weeks.
You can, but it is not ideal. Garden soil compacts in a confined bed and drains poorly. Mix it with compost and perlite, or use a purpose made raised bed mix.
Use logs or branches as hugelkultur filler in the bottom 15 to 20 centimetres, then fill only the top 30 centimetres with soil mix.
Bulk delivery by the cubic yard is usually cheaper once you need about a cubic yard or more. For one small bed, bags avoid a delivery minimum.
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