Soil Volume Converter

Soil volume conversions use liters as the base unit.

Metric conversions:

• 1 cubic meter = 1,000 liters

Imperial conversions:

• 1 cubic foot = 28.3168 liters
• 1 cubic yard = 764.555 liters (27 cubic feet)
• 1 US gallon = 3.78541 liters

Common soil bag sizes:

• Small bag: 0.5 cu ft (14.2 L)
• Medium bag: 1 cu ft (28.3 L)
• Large bag: 2 cu ft (56.6 L)
• Bulk bag: 1 cu yd (764.6 L)

Garden bed examples:

• 4×4 ft raised bed, 6 in deep: 8 cu ft (0.3 cu yd, 227 L)
• 4×8 ft raised bed, 12 in deep: 32 cu ft (1.2 cu yd, 906 L)
• 1×1 m raised bed, 30 cm deep: 0.3 cu m (300 L)

Soil and compost are sold by volume rather than weight for a practical reason: their weight swings wildly with moisture. A cubic foot of dry peat and the same volume soaked with water differ by many pounds, so volume is the only stable way to price and compare growing media.

The economics are worth knowing before a big project. Bagged soil is convenient but expensive per unit; a cubic yard bought in bulk (that’s 27 cubic feet, or roughly 25 to 40 bags) usually costs a fraction of the bagged price. The point where bulk delivery pays off is surprisingly low, often just a few raised beds.

Order about 10% more than the geometry says

Loose soil and compost are full of air. Water them in and they compress, so a bed filled level to the rim in the morning sits an inch or two down by the next day. That is not a rounding error on a deep bed: the 10% allowance the calculator adds to the bag counts above is the difference between finishing the job and a second trip to the garden centre.

Depth is the other thing people underestimate, because volume grows with depth just as fast as it grows with area. Doubling a bed from six inches deep to twelve doubles the soil, the same as doubling its footprint, and it is far less obvious standing in front of it.

What actually goes in the bed

Do not buy the whole volume as bagged potting mix. A workable raised-bed fill is roughly half topsoil, a third finished compost, and the rest something coarse for drainage, and the bottom few inches can be rougher material still: half-rotted leaves, small branches, coarse bark. It settles further than good soil does, so allow for that on top of the 10%, but it costs nothing and it is where the earthworms end up.

One last thing on comparing prices: a bag is not a unit. Work out the cost per cubic foot before deciding, because the same soil often looks cheap by the bag and expensive by volume.