Raised Bed Soil Calculator

Multiply the inside length, width and fill height of the bed to get a volume, then divide by 27 to convert cubic feet into cubic yards. This calculator runs that step directly, adds up multiple identical beds if you have more than one, and splits the total by ingredient once you pick a recipe, so you know how much compost, topsoil, peat moss or vermiculite to actually buy rather than one combined soil figure.

The recipe behind the original square-foot-gardening method created by Mel Bartholomew: equal thirds compost, peat moss (or coconut coir) and coarse vermiculite by volume, with no native soil or topsoil at all. It never compacts, drains well and holds nutrients longer than plain soil, which is why it is the more expensive of the two recipes this calculator offers.

Mel's Mix if budget allows, since it drains well and never compacts. If cost matters more, a topsoil and compost blend at roughly one part compost to two parts topsoil, per University of Maryland Extension guidance, is a solid cheaper alternative, especially over a bed sitting on compacted or clay native ground.

Not by itself. Plain topsoil compacts more than a raised bed needs and lacks the organic matter roots benefit from. University of Maryland Extension recommends blending it with compost, roughly one part compost to two parts topsoil, rather than filling a bed with topsoil alone.

No. Compost by itself lacks the mineral component of real soil and can compact heavily on its own, holding too much water. It needs to be blended with topsoil, peat moss or coir and something like vermiculite, which is exactly what both recipes in this calculator do.

At the common 11 inch fill height this calculator starts with, a single 4 foot by 8 foot bed needs about 2.7 cubic yards. Enter your own dimensions above, since fill height varies by bed design, and the result updates for any bed size or number of beds.

There is no single fixed recommended depth the way there is for a mulch or soil topdressing layer, since a raised bed's fill depth is set by the box itself rather than by what is being planted. Most beds are built 10 to 12 inches tall and filled a little short of the top rim, which is why this calculator asks for fill height directly instead of assuming one standard number.

Enter the dimensions for one bed and the number of identical beds you are filling, and this calculator multiplies for you rather than requiring a separate calculation per bed. If your beds are different sizes, run the calculator once per size and add the results together.

General garden soil is dug into existing ground at a recommended working depth, covered on BunnyCorner's Soil Calculator. A raised bed is a boxed, contained volume with no existing ground to work into, so its soil needs are set by the box's dimensions and filled with a blended recipe like Mel's Mix rather than a single soil product.

It depends on the recipe and bed size. This calculator pre-fills a starting price per cubic yard for each ingredient in whichever recipe you pick, fully editable, so you can drop in your own supplier's prices and get an exact total rather than a market guess.

Ground soil has an existing structure, drainage path and soil life to build on. A raised bed starts as an empty box, so its fill has to do everything on its own: drain well, hold nutrients and avoid compacting under its own weight, which is exactly what a blended recipe like Mel's Mix or a topsoil and compost blend is formulated to do.

Yes. Expect a newly filled bed to settle a few inches over its first season as the organic matter in the mix breaks down and compacts under watering. This is normal, and most raised bed guides recommend topping off with more mix as needed rather than overfilling the bed on day one.

Yes. Length, width and fill height all accept metric or imperial units and convert automatically, and the weight range shown alongside the volume converts to kilograms as well as pounds. The ratios and sourced density behind the numbers stay the same regardless of which units you use.