Raised Bed Soil Calculator

For a standard 4×8 raised bed that's 12 inches deep, you need about 32 cubic feet of soil (roughly 1.2 cubic yards). That's approximately 16 bags of 2-cubic-foot soil. If your bed is only 6 inches deep, you'll need half — about 16 cubic feet. For the best results, fill it with a mix of 60% topsoil, 30% compost, and 10% potting mix or perlite.

A 4×4 raised bed that's 12 inches deep requires about 16 cubic feet (0.6 cubic yards) of soil — roughly 8 bags of 2-cubic-foot soil. If you're building a taller 18-inch bed, you'll need about 24 cubic feet. For a 6-inch deep bed, only 8 cubic feet is needed. Use our calculator above to get exact numbers for your specific dimensions.

The most recommended raised bed soil recipe is 60% topsoil, 30% compost, and 10% potting mix (soilless growing medium). For vegetable gardens specifically, a richer mix of 40% topsoil, 40% compost, and 20% perlite/vermiculite works well. Avoid using more than 20% peat moss as it's acidic. The key is having loose, well-draining soil rich in organic matter so roots can grow freely.

For small projects (under 1 cubic yard / 27 cubic feet), bagged soil is more convenient and easier to handle. For larger projects (2+ cubic yards), bulk delivery is typically 40–60% cheaper. A cubic yard of bulk topsoil costs $25–$50 delivered, while the same volume in 2-cubic-foot bags could cost $120–$150. Our calculator shows both options with cost estimates so you can compare.

Most vegetables need 6–12 inches of soil depth for healthy root growth. Shallow-rooted crops like lettuce and herbs do fine in 6-inch beds. Most vegetables (tomatoes, peppers, beans) prefer 12 inches. Deep-rooted crops like carrots, potatoes, and parsnips need 12–18 inches. If your raised bed sits on native soil, roots can extend below the bed — a 6-inch bed on loosened ground effectively gives you 12–18 inches of growing depth.

For a rectangular bed: multiply length (ft) × width (ft) × depth (ft). Since depth is usually measured in inches, divide inches by 12 first. Example: a 4×8 bed that's 10 inches deep = 4 × 8 × (10/12) = 26.7 cubic feet. For circular beds, use π × radius² × depth. To convert cubic feet to cubic yards, divide by 27. Our calculator handles all these conversions automatically.

Bagged topsoil costs $4–$8 per cubic foot depending on quality and brand. A 2-cubic-foot bag of premium garden soil typically runs $8–$12. Compost is $3–$7 per cubic foot bagged. For bulk delivery, mixed planting soil is $25–$50 per cubic yard (27 cubic feet), making it significantly cheaper for large projects. A typical 4×8×12" bed costs $70–$150 to fill with bagged soil or $30–$60 with bulk soil.

Yes! At the start of each growing season, refresh your existing soil by adding 1–2 inches of compost on top and mixing it into the top few inches. Add granular organic fertilizer (½ cup per 5 square feet) to replenish nutrients. If the soil level has dropped from settling and decomposition, top it off with fresh planting mix. Most raised bed soil lasts many seasons with annual amendments.

Topsoil is natural soil from the top layer of the earth — it's heavy, retains moisture, and provides structure. Garden soil is topsoil enriched with compost and organic matter — ideal for in-ground beds. Potting mix is a soilless blend of peat moss, perlite, and vermiculite — lightweight, well-draining, and sterile. For raised beds, combining all three creates the ideal growing medium: topsoil for structure, compost for nutrients, and potting mix for drainage.

Divide your total cubic feet needed by the bag size. For example, a 4×8×12" bed needs 32 cubic feet: that's 32 one-cubic-foot bags, 22 bags of 1.5 cu ft, 16 bags of 2 cu ft, or 11 bags of 3 cu ft. Most garden centers sell 1.5 or 2 cubic foot bags. Our calculator automatically shows bag counts for all common sizes so you can buy the right amount.

If you're using a compost-rich soil mix, you may not need additional fertilizer right away — compost provides slow-release nutrients. However, adding ½ cup of granular all-purpose organic fertilizer per 5 square feet at planting time gives young plants a strong start. For vegetable gardens, a balanced 10-10-10 or organic equivalent works well. Our calculator estimates the fertilizer needed based on your bed's surface area.

New raised bed soil typically settles 10–20% in the first few months as air pockets collapse and organic matter decomposes. A 12-inch bed might drop to 10 inches. To compensate, either fill your bed a bit higher than needed or plan to top it off after a few weeks. Watering the soil thoroughly after filling and before planting helps speed up initial settling.

A keyhole garden is a circular raised bed (typically 6 feet in diameter) with a wedge-shaped path cut in from the edge to a center compost basket. The basket distributes nutrients as you water. Because of the path cutout and center basket, a keyhole garden needs about 15–20% less soil than a full circle of the same diameter. Our calculator handles the keyhole shape geometry automatically.