How much soil for a raised bed?

Measure the inside length, width, and depth you want to fill. Multiply the measurements in the same units to find the volume.

How much soil does a 4×8 bed hold?

At 12 inches deep, a 4 by 8 foot bed holds 32 cubic feet of soil. That is about 1.19 cubic yards or 22 bags at 1.5 cubic feet each, before any extra allowance.

Rectangular bed = inside length × inside width × soil depth. Convert inches to feet before multiplying.

How do I top off an existing bed?

Subtract the depth of the existing soil from the desired depth. If the same 4×8 bed has 8 inches of fill and you want 12 inches, you need 4 more inches of soil, or about 10.67 cubic feet. Measure at multiple spots if the fill has settled unevenly.

How do I measure a round raised bed?

Measure across the inside at the widest point and divide by two for the radius. Multiply π by radius squared, then multiply by the fill depth.

For example, a round bed with a 3-foot inside diameter and 8 inches of fill depth needs about 4.71 cubic feet. For sloped or curved sides, this is an estimate. Use the manufacturer's volume when available.

Bags, bulk, and mulch

• Bags. Divide the order volume by the volume printed on one bag. Round up to enough whole bags.
• Bulk. Divide cubic feet by 27 to get cubic yards. Ask your supplier which order increments it offers.
• Mulch. Calculate it as its own layer and check that bed walls leave space for it.
• Settling. Order extra if your supplier expects the mix to settle, and keep any leftover soil for later top-offs.

For container formulas and more examples, see Iowa State University Extension’s soil-volume guide.