Calculate soil depth first, then multiply by bed size

A 4-by-8-foot raised bed needs between 32 and 64 cubic feet of soil, depending on how deep you fill it. Most vegetable gardens work at 12 inches deep, which means a 4x8 bed holds 32 cubic feet. If you go 18 inches deep (better for root crops like carrots and potatoes), you need 48 cubic feet. At 24 inches, you need 64 cubic feet.

The math is straightforward: length × width × depth (all in feet) = cubic feet. A 4x8 bed at 12 inches is 4 × 8 × 1 = 32 cubic feet. Soil is sold by the cubic yard, and one cubic yard equals 27 cubic feet, so 32 cubic feet is roughly 1.2 cubic yards. Most garden centers sell soil in bags too — a standard 2-cubic-foot bag means you would need 16 bags for a 12-inch depth.

Key Takeaways

  • A 4x8 raised bed at 12 inches deep requires 32 cubic feet of soil, which is about 1.2 cubic yards or 16 bags of standard 2-cubic-foot soil.
  • Depth matters more than you might think — going from 12 to 18 inches adds 16 cubic feet and costs more, but gives root vegetables room to grow.
  • Bulk soil from a landscape supplier is cheaper per cubic foot than bagged soil, but you need a way to move and spread it.
  • Most raised beds settle over time, so buying 10 to 15 percent extra soil lets you top it off in spring without buying more.

Depth choices and what they mean for your plants

Twelve inches is the minimum for most vegetables — lettuce, spinach, beans, and peppers do fine at this depth. Tomatoes and squash can work at 12 inches if you water regularly, but they prefer 18. Root crops like carrots, beets, and parsnips need at least 12 inches and perform better at 18 or more.

Eighteen inches is the sweet spot for a mixed vegetable garden. It costs 50 percent more soil than 12 inches but gives you flexibility across plant types and reduces watering stress in hot months. Twenty-four inches is overkill for most home gardens — it costs twice as much as 12 inches and the extra depth rarely pays off unless you are growing very deep-rooted perennials or want to minimize watering in an arid climate.

Bulk soil versus bagged soil — cost and logistics

Bagged soil costs $3 to $8 per 2-cubic-foot bag depending on your region and the brand. For a 4x8 bed at 12 inches, you need 16 bags, which runs $48 to $128. The advantage is you can buy it gradually and don't need heavy equipment. The disadvantage is you spend hours opening and pouring bags.

Bulk soil from a landscape supplier or mulch yard costs $25 to $50 per cubic yard delivered, depending on your location and whether you pick it up or have it delivered. For 1.2 cubic yards, that is roughly $30 to $60 total — less than half the bagged price. The catch is you need a wheelbarrow and shovel, and the supplier may have a minimum order (often 3 to 5 cubic yards). If you are building multiple beds or have neighbors willing to split an order, bulk is almost always cheaper.

What type of soil to buy

Garden centers sell three main products: topsoil, garden soil, and potting mix. Topsoil is the top layer of native soil, usually screened to remove rocks and roots. It is cheap but often compacts over time and may contain weed seeds. Garden soil is topsoil blended with compost and sometimes peat moss or coconut coir — it drains better and holds nutrients longer. Potting mix is lightweight and fluffy, designed for containers, and costs two to three times more than garden soil.

For a raised bed, garden soil is the standard choice. It costs more than plain topsoil but less than potting mix, and it performs well for vegetables. Many gardeners mix topsoil and compost 70-30 or 80-20 to save money while keeping drainage and fertility decent. If you buy bulk, ask the supplier what they have — many landscape yards sell a "garden mix" or "raised bed mix" that is already blended.

Account for settling and plan to refresh

Soil settles after the first season, especially if you water heavily or walk on the bed. You can lose 1 to 3 inches of depth in the first year. To avoid running short, buy 10 to 15 percent extra — for a 32-cubic-foot bed, that means ordering 35 to 37 cubic feet instead. This extra soil also gives you material to top off the bed each spring before planting.

Over time, organic matter breaks down and the soil becomes denser. Many gardeners add 2 to 4 inches of compost or aged manure to the top of the bed each year. This is cheaper than replacing all the soil and keeps the bed productive longer.

Soil calculator for other bed sizes

If your bed is a different size, use this formula: length (feet) × width (feet) × depth (feet) ÷ 27 = cubic yards. A 3x6 bed at 12 inches is 3 × 6 × 1 ÷ 27 = 0.67 cubic yards (about 18 cubic feet, or 9 bags). A 4x4 bed at 18 inches is 4 × 4 × 1.5 ÷ 27 = 0.89 cubic yards (about 24 cubic feet, or 12 bags). A 2x8 bed at 12 inches is 2 × 8 × 1 ÷ 27 = 0.59 cubic yards (about 16 cubic feet, or 8 bags).

When you call a supplier or visit a garden center, tell them the cubic feet or cubic yards you need. Most will round up to the nearest half or full yard, so asking for 1.2 cubic yards usually means they deliver 1.5.

Where to buy soil and what to expect

Local landscape supply yards, mulch yards, and quarries usually offer the best bulk prices and can deliver or let you pick up. Home Depot and Lowe's sell bagged soil and garden soil by the pallet if you need volume. Local garden centers often have both bagged and bulk options and can advise on what grows well in your region. Soil delivery typically takes 3 to 7 days depending on the supplier's schedule.

If you order bulk, ask whether the price includes delivery or if you pick it up. Some suppliers charge extra for delivery under a certain amount, so a 3-yard order might cost $75 to $100 delivered, while a 1.5-yard order could cost $50 to $80 because of a delivery fee. Picking up yourself saves money but requires a truck or trailer.

Frequently Asked Questions

Can I use just compost instead of a soil and compost mix?

Pure compost drains too fast and compacts quickly, leaving your plants thirsty by mid-summer. A mix of 70 to 80 percent garden soil and 20 to 30 percent compost works better. If you use only compost, you will water constantly and refill the bed every season.

Do I need to put cardboard or landscape fabric on the bottom?

Cardboard kills weeds for the first season but breaks down after that. Landscape fabric lasts longer but can trap water and roots sometimes struggle to penetrate it. Many gardeners skip both and just pull weeds as they come up — it takes 10 minutes a week and costs nothing.

What if I want to fill the bed gradually?

You can fill it in stages, but the bed will settle unevenly. If you fill it halfway one week and finish the next, the first half will compact more than the second, leaving a dip. Better to fill it all at once and let it settle for a week before planting.

Is bagged soil from big-box stores as good as bulk soil from a landscape yard?

Quality varies by brand and supplier. Big-box bagged soil is often lighter and fluffier because it contains more peat or coir, which drains well but breaks down faster. Bulk soil from a landscape yard is usually heavier and denser, with more mineral content, which settles more but lasts longer. Both work — it depends on your budget and how often you want to refresh the bed.

How much does a cubic yard of soil weigh?

Dry soil weighs about 1,200 to 1,400 pounds per cubic yard. Wet soil weighs 1,600 to 2,000 pounds. This matters if you are moving it yourself — 1.2 cubic yards of moist soil is roughly 2,000 pounds, which is heavy enough to need a wheelbarrow and multiple trips.