How much soil do I need for a 4x8 raised bed?
Check it with your own numbers
Open the Topsoil Calculator with these values
| Length | 8 ft |
| Width | 4 ft |
| Depth | 12 in |
| Topsoil needed | 1.19 yd³ |
| Approx. weight | 1.3 tons |
| 1 ft³ bags | 32 |
The volume
4 × 8 × 1 ft = 32 cubic feet. That converts to 1.19 yd³ and weighs about 1.3 tons. If you buy bags, you need 32 of the 1 ft³ size. Bagged "raised bed mix" is often sold in 1.5 or 2 ft³ bags, so divide accordingly.
Don't fill it with straight topsoil
Plain topsoil compacts in a raised bed and drains poorly. The standard mix that most extension services recommend is roughly:
- 60% screened topsoil
- 30% compost
- 10% coarse material such as perlite, pine fines or aged bark
For one 4x8 bed that works out to about 19 ft³ of topsoil, 10 ft³ of compost and 3 ft³ of the coarse stuff.
Bags or bulk?
Thirty-two bags is a lot of plastic and a lot of money for one bed. If you are filling two or more, bulk becomes the obvious choice. A garden center that sells blended raised-bed soil by the yard can drop 2 or 3 yards in your driveway, enough for two or three beds of this size.
Fill the bottom cheaply
Vegetables need about 8 to 12 inches of good soil. If your bed is taller than 12 inches, or if you want to save on soil, you can fill the bottom with logs, branches and leaves. This is sometimes called hugelkultur. Just expect the level to drop a few inches over the first year as the wood breaks down.
Settling
Fresh mix settles 10 to 20%. Fill the bed to the top, water it well, and top it off a week later. Plan on adding 2 inches of compost each spring after that.
Line the bottom?
Hardware cloth on the bottom keeps gophers and voles out. Skip plastic liners on the floor; they trap water.
For other sizes, use the full Topsoil Calculator or browse all answers.