Raised Bed & Garden Soil Calculator

How to calculate soil volume for a raised bed

Measure the usable internal dimensions of the bed and the depth you intend to fill with soil. Use internal dimensions because the soil occupies the space inside the bed walls.

1. Choose the bed shape: Select rectangular/square or circular.
2. Enter the dimensions: For a rectangular bed, enter internal length, width, and soil-fill depth. For a circular bed, enter the internal diameter and depth.
3. Review geometric volume: This is the volume of the space to be filled before any optional purchase allowance.
4. Choose a bag size: Select a listed bag volume or enter a custom bag size. Actual product sizes vary, so check the bag label.
5. Optionally add extra material: A user-selected allowance increases the estimated purchase quantity. It is a planning choice, not a universal settling factor.
6. Choose a soil blend: If using a preset recipe, the calculator allocates the planned volume among its ingredients by relative parts.

Soil volume formulas

For a rectangular or square bed, volume equals internal length × internal width × soil-fill depth. For a circular bed, volume equals π × radius² × soil-fill depth, where radius is half the internal diameter. Keep all dimensions in the same unit before calculating.

One cubic yard equals 27 cubic feet. A bag count is calculated by dividing the purchase-planning volume by the selected bag volume and rounding up to the next whole bag.

Choosing a bag size

Bag sizes vary by material, product, and retailer. Use the volume printed on the bag rather than assuming every topsoil, compost, or raised-bed mix uses the same size. If your bag size is not listed, select Custom and enter its volume in cubic feet.

Optional extra-material allowance

The allowance is an optional purchase-planning buffer for factors such as spillage, uneven filling, or a planned top-up. It is separate from the geometric volume and should not be interpreted as a universal recommendation for soil settlement or compaction.

Using a soil blend

Recipe presets divide the planned volume by relative ingredient parts. For example, a 60/30/10 blend allocates 60% to topsoil, 30% to compost, and 10% to an aeration material. These are planning ratios, not guaranteed growing-media prescriptions; select ingredients based on the plants, local materials, drainage, and soil guidance appropriate to your garden.

Bagged soil or bulk delivery?

Compare the total cost of the required bag volume with a local bulk quote that includes delivery and any minimum order. There is no universal volume at which bulk soil is always cheaper; the break-even point depends on local prices, delivery charges, and the product being purchased.

Calculating topsoil, fill dirt, and garden soil

Whether calculating bulk topsoil, specialized garden blends, or fill dirt, the volume formula is identical: multiply internal length by width by depth. One cubic yard always equals 27 cubic feet. For standard bed sizes such as a 4 × 8 ft bed (32 ft³ or ~1.19 yd³) or a 4 × 4 ft bed (16 ft³ or ~0.59 yd³), use our quick presets above.

Need guidance on soil depth, settling allowances, or bag count tables? Read our companion guide on How Much Soil Do I Need for a Raised Bed. If you are blending topsoil, compost, and aeration amendments, explore our guide to the Best Soil Mix for Raised Beds.

What this calculator does not estimate

The calculator estimates volume, not weight. Soil and compost weight vary substantially with composition, particle size, and moisture content, so a reliable weight estimate requires material-specific density information.