How Much Soil Does a Raised Bed Need? Simple Math and Lighter Ways to Fill

Filling a raised bed is often the part that surprises people: it can take far more soil, and far more bags, than you'd guess. Here's how to work out your number before you shop, plus what two garden companies suggest for filling a tall bed without buying all of it. Product facts come from the sellers' own pages, checked on October 23, 2026. Prices change often, so check the page before you buy.

The one formula you need

Multiply length times width times depth, all in feet, and you get cubic feet. Vego Garden's soil guide gives the same formula and reminds you to convert inches first: a 17" bed is 17 divided by 12, or about 1.4 feet. To turn cubic feet into cubic yards (how bulk soil is usually sold), divide by 27.

• 3' x 6' bed with 10" sides: 3 x 6 x 0.83 = about 15 cubic feet. Gardener's Supply's soil guide uses this same example and also lands on 15 cubic feet.
• 4' x 8' bed, 17" tall: 4 x 8 x 1.42 = about 45 cubic feet. Vego's product page answers this exact question with 45 cubic feet (1.2 cubic yards), or 30 bags if each bag holds 1.5 cubic feet.
• 2' x 4' elevated planter with 8" of soil: 2 x 4 x 0.67 = about 5.3 cubic feet, roughly 160 quarts. (That's our arithmetic, using 1 cubic foot is about 30 quarts.)

Gardener's Supply suggests rounding up rather than down; its example is rounding 0.444 cubic yards up to half a yard. It also says the soil level ideally sits within an inch or so of the rim.

Watch the bag size

Bags are sold in quarts or cubic feet, and it's easy to mix them up. A 20-quart bag holds about two-thirds of a cubic foot. For example, Gardener's Supply's Organic Raised Bed Potting Mix is one 20-quart bag weighing 21 lbs, listed at $29.99 when we checked (the page also showed a "quantity selected exceeds current stock" notice and says it can't ship to AE, AK, GU, HI or PR). Before you count bags, divide your cubic feet by the bag's own cubic-foot size.

One small thing we noticed: Gardener's Supply's 3' x 6' example lists "9 cubic feet of topsoil (9 20-quart bags)," which treats a 20-quart bag as one cubic foot. If you're buying 20-quart bags, you'd likely need about half again as many as that line suggests.

What goes in the mix

Both companies suggest a similar starting blend: about 60% topsoil, 30% compost and 10% soilless potting mix. Gardener's Supply adds that if you can't get good topsoil, a 50-50 blend of soilless mix and compost is an acceptable substitute, and that peat moss shouldn't be more than 20% of the mix. If you have several beds to fill, it suggests buying in bulk by the cubic foot or yard.

Filling a tall bed without buying all of it

A waist-high bed saves bending, but filling it to the top with bagged soil is a lot to buy and haul. Vego Garden's guide describes a layered approach called hugelkultur: logs and thick branches at the bottom, then leaves, grass clippings, straw and kitchen scraps, and compost with raised bed soil on top. In its words:

• In a 32" bed, the wood layer can be up to 15" deep. In a 17" bed, keep the wood base to about 6".
• Vegetables need at least 8 to 12 inches of good soil above the filler, and root crops like carrots and potatoes at least 12 inches.
• Use hardwoods such as oak, maple or birch, and avoid black walnut and treated wood.
• Water the layers as you go so they settle into the gaps.
• Vego says this can replace 40 to 60% of the purchased soil. That's the company's own estimate, not something we measured.

Here's how that plays out on paper for a 3' x 6' bed that's 32" deep: the whole bed is about 48 cubic feet, and with a 15" layer of wood and yard waste, the soil above it is about 25.5 cubic feet. Expect the bed to settle as the bottom layers break down, so plan to top it up.

Making the job easier on your back

• Smaller bags weigh less per trip. Compare the listed weight on the bag or product page before you buy.
• For a big bed, bulk delivery means no bags to lift at all; just shovel from the pile into a cart.
• Many stores will load bags into your car if you ask, and a garden cart saves carrying them across the yard.
• Elevated planters on legs or wheels hold much less soil than a deep bed. See our guides to elevated garden beds and raised beds on wheels.

Sources

• Gardener's Supply: How Much Soil Do I Need? (opened 2026-10-23)
• Gardener's Supply: Organic Raised Bed Potting Mix, 20 Quart (opened 2026-10-23)
• Vego Garden: How To Fill Raised Garden Beds With Soil And Save Money (opened 2026-10-23)
• Vego Garden: 32" Extra Tall 6 in 1 Modular Raised Garden Bed Kit (FAQ on soil for a 4' x 8' bed) (opened 2026-10-23)
• Vego Garden: How Much Soil Do I Need for a Raised Garden Bed? (opened 2026-10-23)