How Much Soil Do You Need for a Raised Bed?
By the TapeMeasureCalc team · Updated · 6 min read
A new raised bed always swallows more soil than you expect. A single 8 × 4 ft bed filled a foot deep holds 32 cubic feet, which is over twenty bags from the garden centre. This guide shows how to work out the volume, choose between bags and a bulk delivery, and cut the cost of filling deep beds.
Work out the volume
Measure the inside of the bed, because thick timber or block walls take up space.
Volume = Length × Width × Soil depth
Use the depth of soil, not the height of the walls. Most people stop an inch or two below the top so mulch and water don’t spill over.
| Bed | Soil depth | Volume |
|---|---|---|
| 4 × 4 ft | 10 in | 13.3 ft³ (0.49 yd³) |
| 8 × 4 ft | 12 in | 32 ft³ (1.19 yd³) |
| 2.4 × 1.2 m | 300 mm | 0.864 m³ (864 litres) |
Bags or bulk?
Divide the volume by the bag size and round up. Two 8 × 4 ft beds a foot deep need 64 ft³: that’s 43 bags of 1.5 ft³, or 32 bags of 2 ft³. In metric, the 864-litre bed above takes 18 bags of 50 litres.
The same 64 ft³ is 2.37 cubic yards. At that size a bulk delivery is usually cheaper and certainly easier on your back, even with a delivery charge. Bags make more sense for one small bed, for topping up, or where a truck can’t get close.
Working out a soil mix
If you’re blending your own, split the total volume by your recipe. For example, a mix of 60% topsoil and 40% compost in a 32 ft³ bed means 19.2 ft³ of topsoil and 12.8 ft³ of compost. The right recipe depends on what you’re growing and the materials available locally, so treat the percentages as your own choice rather than a rule.
Filling deep beds for less
Most vegetables do fine in 10 to 12 inches of good soil. If your bed is 24 inches tall, you don’t have to buy two feet of soil. Many gardeners fill the bottom third or half with coarse organic material such as small logs, branches and leaves, then put good soil on top. In an 8 × 4 ft bed, filling the bottom 12 inches that way saves 32 ft³ of soil.
The organic layer breaks down over a few seasons, so expect the surface to sink and plan on topping up.
Allow for settling
New, fluffy soil settles once it’s watered and walked around, especially mixes with plenty of compost. Some people buy 5 to 10% extra on day one. Others fill to the calculated amount and top up later with compost, which feeds the bed at the same time. Either way works; just don’t be surprised when the level drops.
Do it with the calculators
The raised bed soil calculator handles several bed sizes at once, with bag counts and bulk pricing side by side. Mulching afterwards? The mulch calculator uses the same bed measurements. For anything else measured in cubic feet or litres, try the cubic feet calculator.