Raised Bed Soil Calculator

How Much Soil Do I Need for a Raised Bed?

The answer depends on three numbers: your bed’s length, width, and how deep you want to fill it. Most raised beds do best at 8–12 inches of soil depth. That gives vegetable roots room to spread without hitting compacted native soil underneath. Shallow beds (under 6 inches) restrict root growth for most crops; go at least 10–12 inches for tomatoes, peppers, and root vegetables.

Once you have the volume in cubic feet, divide by 27 to get cubic yards — the unit bulk suppliers quote in. For bagged soil, divide by the bag size (typically 1.5 or 2 cubic feet) and round up to the nearest whole bag.

Don’t fill with straight topsoil or garden soil pulled from the ground. It compacts in a raised bed, drains poorly, and stunts plant growth. The standard raised bed soil mix ratio is 60% topsoil, 30% compost, and 10% perlite or coarse sand. This blend holds moisture, drains excess water, and provides the organic matter vegetables need. If you’re buying a pre-mixed “raised bed mix” in bags, it usually approximates this ratio — check the label. Use our Compost Calculator to figure out exactly how much you’ll need.

For large beds (more than 2–3 cubic yards), get a bulk quote from a local landscape supplier. Bagged soil costs 3–5x more per cubic foot than bulk once you factor in delivery. The calculator above shows your total in cubic yards so you can compare both options easily.

Worked Example

Let’s walk through a 4×8 foot raised bed filled to 10 inches deep — a very common setup.

1. Area: 4 ft × 8 ft = 32 square feet.
2. Convert depth to feet: 10 inches ÷ 12 = 0.833 feet.
3. Cubic feet: 32 sq ft × 0.833 ft = 26.7 cubic feet of soil.
4. Cubic yards: 26.7 ÷ 27 = ~0.99 cubic yards (round to 1 yard for a bulk order).
5. Bags (1.5 cu ft): 26.7 ÷ 1.5 = 17.8 → 18 bags.
6. Bags (2 cu ft): 26.7 ÷ 2 = 13.35 → 14 bags.
7. Estimated weight: 26.7 cu ft × 53.3 lbs/cu ft ≈ ~1,423 lbs.

So for a 4×8 bed at 10 inches, you need roughly 26.7 cubic feet, 1 cubic yard, or about 18 standard bags of 1.5 cu ft soil. Add 10–15% extra to account for settling — soil always compresses after the first watering.

Common Mistakes

• Not accounting for settling. Loose bagged soil can settle 10–20% after the first good rain. Fill slightly past your target depth and let it settle before planting, or plan to top off in spring.
• Using straight garden soil. Native soil pulled from your yard compacts in a raised bed into a dense, poorly draining block. Always use a proper raised bed mix or at minimum blend in compost and perlite.
• Ignoring the compost ratio. Under-composted soil runs out of nutrients fast. At least 25–30% by volume should be mature compost. More is fine; less means more fertilizing all season.
• Underestimating depth. A 4-inch-deep bed is barely a planter box. For productive vegetable growing, shoot for 10–12 inches minimum. Shallower beds heat up faster, dry out quicker, and stunt deep-rooted crops.
• Buying bagged past the bulk threshold. Once your order exceeds about 2 cubic yards (54 bags), bulk delivery from a landscape yard almost always beats bagged. Get a quote before you load up a cart at the garden center.

Sources & further reading

Soil depth and mix ratio guidance in this article draws on general recommendations from university cooperative extension services and widely published raised bed gardening resources. For more on how we build and verify the formulas behind every calculator on this site, see our methodology page.

Last updated: July 8, 2026.