Calculate soil volume by bed dimensions

The amount of soil you need depends on three measurements: the length, width, and depth of your raised bed. Multiply those three numbers together to get cubic feet, then convert to cubic yards if you're ordering in bulk. A bed that is 4 feet long, 2 feet wide, and 12 inches deep holds 8 cubic feet of soil—which is roughly 0.3 cubic yards.

Most raised beds are 12 inches (1 foot) deep, though some are 18 or 24 inches. Deeper beds let roots go further and hold more moisture, but they also require more soil and cost more to fill. If you're building your own bed, 12 inches is a practical starting point for vegetables and herbs.

Use this formula: length (feet) × width (feet) × depth (feet) = cubic feet. Then divide cubic feet by 27 to get cubic yards. For example, a 4×8×1 bed needs 32 cubic feet, or about 1.2 cubic yards.

Key Takeaways

  • Multiply your bed's length, width, and depth in feet to find cubic feet, then divide by 27 to convert to cubic yards for ordering.
  • A standard 4×8×1 foot bed holds roughly 1.2 cubic yards, or about 32 cubic feet of soil.
  • Soil settles after watering, so fill your bed slightly higher than the rim and expect it to drop 1 to 2 inches over the first month.
  • Bulk soil from a landscape supplier is cheaper per cubic yard than bagged soil, but bagged soil works for small beds under 50 cubic feet.
  • Mix topsoil, compost, and other amendments rather than using one type alone, so roots have better drainage and nutrient access.

When to order bulk soil versus bags

If your bed is smaller than 50 cubic feet (about 2 cubic yards), bagged soil is usually simpler and costs less in total. A standard bag holds 2 cubic feet, so an 8-cubic-foot bed needs four bags. Bags are straightforward to carry, store, and mix, and you can buy them at a garden center or hardware store the same day.

For beds larger than 50 cubic feet, bulk soil from a landscape supplier becomes cheaper per cubic foot. A landscape supplier delivers by the cubic yard and can mix custom blends—topsoil with compost already stirred in, for instance. Delivery usually costs $50 to $150 depending on distance, but you save money on the soil itself if you're filling multiple beds or a large one.

Call landscape suppliers in your area and ask for their price per cubic yard for a topsoil-compost blend. Compare that to the per-cubic-foot cost of bagged soil at your garden center. If you're on the fence between bulk and bags, bulk usually wins at 1.5 cubic yards or more.

Account for soil settling and compaction

Soil settles after you water it, especially in the first few weeks. Fill your bed to about 1 to 2 inches above the rim, because the soil will drop as it compacts and as organic matter breaks down. After a month of watering and planting, expect the level to be roughly 1 inch lower than where you started.

This settling is normal and happens faster with compost-heavy mixes than with pure topsoil. If you fill your bed level with the rim on day one, it will look half-empty by mid-season. Overfilling slightly at the start saves you from buying more soil later.

Mix soil types instead of using one alone

The best raised bed soil is a blend, not a single product. A common mix is 40% topsoil, 40% compost, and 20% other amendments like peat moss, coconut coir, or aged bark. This blend drains well, holds moisture without waterlogging, and gives roots access to nutrients.

Pure topsoil alone compacts too much and drains poorly. Pure compost breaks down quickly and settles fast. Mixing them gives you the structure of topsoil and the nutrition of compost. If you order bulk soil, ask the supplier to mix topsoil and compost for you—many do this at no extra charge.

For a 4×8×1 bed (32 cubic feet), you might order 13 cubic feet of topsoil, 13 cubic feet of compost, and 6 cubic feet of peat moss or coir. If buying bags, buy them in those proportions and mix them in the bed as you fill.

Common mistakes that waste soil or money

The most common mistake is filling the bed completely level with the rim. Soil settles, so you end up with a gap and have to buy more. Fill slightly high and accept that settling is normal.

Another mistake is ordering bulk soil without checking the delivery fee. A $40-per-yard soil can cost $150 total once delivery is added. Always ask the full delivered price before ordering.

A third mistake is using only compost or only topsoil. Compost alone breaks down too fast and leaves you with a sunken bed by next year. Topsoil alone is too dense and doesn't drain well. Always mix at least two types.

Finally, some people order soil without measuring their bed first. Measure twice, calculate once, and add 10% extra to account for settling. Ordering too little means a second trip; ordering too much means leftover soil you have to store or haul away.

Refill and amend soil each season

After the first year, your soil will have settled and organic matter will have broken down. Add 2 to 4 inches of fresh compost or topsoil-compost blend on top each spring before planting. This keeps the bed at the right depth and replaces nutrients that plants used the year before.

You do not need to empty and refill the entire bed every year. Top-dressing with fresh material is faster and cheaper. Over time, the bottom layers become dense and compacted, so every three to five years it makes sense to empty the bed, loosen the soil underneath, and refill with fresh material.

Frequently Asked Questions

How many bags of soil do I need for a 4x8 raised bed?

A 4×8 bed that is 12 inches deep holds 32 cubic feet. Standard bags hold 2 cubic feet, so you need 16 bags. If your bags are labeled differently (some say "covers X square feet"), check the cubic footage on the label. Buying 18 bags accounts for settling.

Can I use garden soil instead of topsoil in a raised bed?

Garden soil is heavier and compacts more than topsoil, and it often contains clay that drains poorly in a raised bed. Topsoil is lighter and better for drainage. If you use garden soil, mix it with compost and peat moss to improve drainage and prevent waterlogging.

What if I don't fill the bed all the way to the top?

Shallower soil means shallower roots. Most vegetables need 12 inches minimum; root crops like carrots and beets need 12 to 18 inches. If your bed is 24 inches deep but you only fill it 12 inches, you're wasting the depth. Fill it fully and use the extra depth for better root growth.

Should I put cardboard or landscape fabric on the bottom?

Cardboard or landscape fabric blocks weeds from below and keeps soil from mixing with native soil underneath. It is not required, but it helps if your raised bed sits on grass or weedy ground. If you use it, lay it down before filling with soil. It will break down over a few years, which is fine—by then roots will be established.

How often should I replace the soil completely?

You do not need to replace it every year. Top-dress with 2 to 4 inches of compost each spring. Every three to five years, empty the bed, loosen the compacted soil underneath, and refill with fresh material. This keeps the bed productive without the cost and labor of annual replacement.