Free Raised Bed Soil Calculator

🌱 FREE GARDEN TOOL

Raised Bed Soil Calculator

Work out exactly how much soil your raised bed needs — in cubic feet, cubic yards, bags and litres — so you buy the right amount the first time, with no waste and no second trip.

✓ Free & instant   ✓ Imperial & metric   ✓ No sign-up needed

🧮 Soil Calculator

Please enter a length, width and depth greater than zero.

Your Results

Soil volume—
Cubic yards—
Order by the yard for large beds — 1 cubic yard = 27 cubic feet.
Bags needed—
Estimated weight—
Moist topsoil weighs about 40 lb (18 kg) per cubic foot.
Your bed preview will appear here

How to Calculate Raised Bed Soil

The formula is simple: Length × Width × Depth = Volume. Measure the inside of your bed, not the outside — timber and metal sides can steal 2–3 inches. Convert depth to feet first (divide inches by 12), then divide cubic feet by 27 to get cubic yards.

Worked example: an 8 ft × 4 ft bed, 12 inches deep: 8 × 4 × 1 ft = 32 cubic feet. That is 32 ÷ 27 = 1.19 cubic yards, or 22 bags of 1.5 cu ft soil. With the recommended 10% extra for settling, order about 35 cubic feet (1.3 cubic yards).

CropMinimum soil depthBest depth
Lettuce, herbs, radishes6 in (15 cm)8 in (20 cm)
Carrots, beets, onions10 in (25 cm)12 in (30 cm)
Tomatoes, peppers, squash12 in (30 cm)18 in (45 cm)
Potatoes12 in (30 cm)18–24 in (45–60 cm)

Common Mistakes to Avoid

  • Measuring the outside of the bed — always measure inside dimensions, where the soil actually goes.
  • Forgetting settling — fresh soil settles 10–20% in the first few weeks. Fill beds a little proud and top up later.
  • Filling the whole bed with topsoil — for deep beds, fill the bottom half with logs, straw or coarse compost (hügelkultur style) and use good soil on top.
  • Buying by the bag for a big bed — once you need more than about 1 cubic yard, bulk delivery is usually far cheaper per cubic foot.
💡 Pro tip: A good raised-bed mix is roughly 60% topsoil, 30% compost and 10% perlite or coarse sand. Mix it in the bed, water it well, and let it settle for a few days before planting.

Frequently Asked Questions

At 12 inches deep, a 4×8 ft bed needs 32 cubic feet of soil — 22 bags of 1.5 cu ft, or 32 bags of 1 cu ft. Add 10% extra (about 3–4 more bags) for settling.
Divide cubic feet by 27. A 4×8 ft bed at 12 in deep is 1.19 cubic yards; at 18 in deep it is 1.78 cubic yards.
Native garden soil can be heavy and may compact. It works best mixed with compost (about one-third compost) and a little perlite for drainage.
Most vegetables need at least 12 inches of good soil. Shallow-rooted greens manage with 6–8 inches, while tomatoes and root crops do best at 18 inches or more.
Usually not — open bottoms let worms in and water drain out. Use hardware cloth (½-inch mesh) only if burrowing pests are a problem.

Related Garden Tools

Plan the rest of your bed with our Mulch Calculator, Potting Soil Matrix and Compost Estimator — or check plant spacing first with the Vegetable Plant Spacing Calculator. See all tools on the Free Tools page.