Calculate soil volume by bed dimensions
The amount of dirt you need depends on 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 equals about 0.3 cubic yards.
Most garden soil is sold by the cubic yard. One cubic yard fills a bed roughly 3 feet by 3 feet by 12 inches deep, or 4 feet by 2 feet by 12 inches deep. Bags of potting mix or garden soil typically hold 2 cubic feet and weigh 40 to 50 pounds, so an 8-cubic-foot bed needs four bags.
Depth matters more than people expect. A 6-inch bed needs half the soil of a 12-inch bed with the same footprint. If you're growing shallow-rooted plants like lettuce or herbs, 6 inches works. Root vegetables, tomatoes, and peppers need 10 to 12 inches minimum.
Key Takeaways
- Multiply length × width × depth in feet to find cubic feet, then divide by 27 to convert to cubic yards for bulk orders.
- A standard 4-by-2-foot bed at 12 inches deep holds about 8 cubic feet, or roughly 0.3 cubic yards, or four 2-cubic-foot bags.
- Shallow beds (6 inches) work for lettuce and herbs; deeper beds (10 to 12 inches) are necessary for tomatoes, peppers, and root crops.
- Bulk soil from a landscape supplier costs less per cubic yard than bagged soil but requires delivery or a truck to haul it home.
Bagged soil versus bulk delivery
Bagged soil is convenient for small beds or when you don't have a truck. A single bag weighs 40 to 50 pounds and costs $3 to $8 depending on the brand and where you buy it. For an 8-cubic-foot bed, you'll spend $12 to $32 on bags alone, plus tax. The downside is that bags take up space, create waste, and the soil settles over time, so you may need to top it off after a few weeks.
Bulk soil from a landscape supply yard or soil company costs $25 to $50 per cubic yard delivered, depending on your location and the type of soil. A truckload typically holds 10 to 15 cubic yards. If you need less than 5 cubic yards, delivery fees may make bulk uneconomical. Call local suppliers for quotes—prices vary widely by region.
Bagged soil is usually a blend of peat moss or coco coir, compost, and perlite or vermiculite. Bulk garden soil is often topsoil mixed with compost. For raised beds, a blend with compost and perlite drains better than plain topsoil, which can compact and hold water. If you order bulk, ask whether it includes compost and what the drainage is like.
Account for settling and amendments
Soil settles after watering and over the growing season. Plan to add 10 to 15 percent extra to account for this drop. If your calculation shows you need 8 cubic feet, buy 9 or 10 cubic feet to start. After the first season, you'll top it off with 1 to 2 inches of fresh compost each year.
Many gardeners mix their own blend instead of buying pre-made soil. A common recipe is one-third compost, one-third peat moss or coco coir, and one-third perlite or coarse sand. This approach costs less for large beds and gives you control over drainage. You'll still need to calculate the total volume first, then divide it into thirds to know how much of each ingredient to buy.
Raised bed size and soil needs at a glance
| Bed Dimensions | Depth | Cubic Feet | Cubic Yards | Bags (2 cu ft each) |
|---|---|---|---|---|
| 2 ft × 2 ft | 12 in | 4 | 0.15 | 2 |
| 4 ft × 2 ft | 12 in | 8 | 0.3 | 4 |
| 4 ft × 4 ft | 12 in | 16 | 0.6 | 8 |
| 8 ft × 4 ft | 12 in | 32 | 1.2 | 16 |
| 4 ft × 2 ft | 6 in | 4 | 0.15 | 2 |
Ordering tips to avoid waste and shortage
Measure your bed's interior dimensions, not the outside frame. A bed that looks 4 feet wide on the outside may be 3 feet 10 inches inside. Round up slightly when you calculate—it's better to have a little left over than to run short halfway through filling.
If you're ordering bulk soil, confirm delivery timing before you order. Some suppliers deliver within a week; others take longer. Have your site ready: clear the area, level the ground, and make sure the truck can reach it. Bulk soil is heavy and will damage grass or soft ground if left sitting.
For bagged soil, check the weight limit on your vehicle before loading. A pickup truck can usually handle 15 to 20 bags, but a sedan cannot. Plan multiple trips if needed, or ask the store whether they offer delivery for a fee.
Soil quality and what to look for
Garden soil and potting mix are not the same thing. Potting mix is lighter, drains faster, and is meant for containers. Garden soil is heavier and better for raised beds because it holds moisture longer and costs less. If you use potting mix in a raised bed, you'll water more often and spend more money.
Check the bag or ask the supplier what's in the soil. Look for compost, peat moss or coco coir, and perlite or vermiculite. Avoid bags labeled only "topsoil"—that's often just excavated dirt with little nutrition. Bags should list the contents and sometimes a may provide analysis showing nitrogen, phosphorus, and potassium percentages.
If you're filling a large bed, consider a soil test. Many county extension offices offer testing for $10 to $30. A test tells you the pH, nutrient levels, and texture, so you know whether to amend before planting. This is especially useful if you're reusing soil from a previous season or mixing your own blend.
Frequently Asked Questions
Do I need to fill the entire bed with expensive potting mix?
No. Use garden soil or a bulk blend for the bottom two-thirds, then top with 3 to 4 inches of compost or potting mix. This saves money and still gives plants good growing conditions. Roots will reach into the lower layers, so the quality matters throughout, but you don't need premium mix everywhere.
Can I reuse soil from last year?
Yes, but refresh it. Remove the top 2 inches and replace it with fresh compost to add nutrients and organic matter. Old soil compacts over time, so loosening it and mixing in compost improves drainage and root growth. If you had disease problems last year, replace more of the soil or let it sit unused for a season.
What if my bed is an odd shape, not a rectangle?
Measure the average length and width, then multiply as usual. For a circular bed, measure the diameter, divide by 2 to get the radius, then use the formula π × radius squared × depth. For an irregular shape, sketch it on graph paper and count the squares to estimate area, then multiply by depth.
How deep should a raised bed be for growing vegetables?
Leafy greens and herbs need 6 inches. Tomatoes, peppers, squash, and beans need 10 to 12 inches. Root vegetables like carrots and beets need 12 inches or more depending on the variety. Shallow beds cost less to fill but limit what you can grow, so choose depth based on what you plan to plant.
Is it cheaper to buy soil in bulk or bags?
Bulk is cheaper per cubic yard—usually $25 to $50 versus $3 to $8 per 2-cubic-foot bag. But for beds under 5 cubic yards, delivery fees and minimum orders make bags more practical. Get quotes from local suppliers; prices vary by region and soil type.