Raised bed soil calculator

How much soil do several raised beds need?

Calculate the volume of each distinct bed size, multiply it by the number of identical beds, then add the groups. Keeping the groups separate makes it easier to check a plan with different widths, depths or shapes.

The input is the soil layer you need to add. A 24-inch-high frame does not necessarily need 24 inches of new soil. If existing soil already occupies 18 inches and you want a final level at 22 inches, calculate a 4-inch refill. For a new empty bed, use the intended soil depth rather than automatically filling to the rim.

The rectangular and round bed formulas

Iowa State University Extension’s raised-bed guidance uses length × width × depth in feet and then divides by 27 for cubic yards. Its 4-by-8-foot example at 12 inches deep holds 32 cubic feet. The round option substitutes the area of a circle for length × width.

The metric setting accepts length and width in meters and depth in centimeters. It computes the same physical volume and displays both cubic meters and the cubic-foot/yard equivalents. Switching settings converts the measurements you have already entered.

Worked example: two rectangular beds and one round bed

Suppose two beds are each 8 feet long and 4 feet wide, with a planned soil layer 12 inches deep. One holds 32 cubic feet, so the pair needs 64 cubic feet. A round bed with a 6-foot inside diameter and a 6-inch layer adds π × 3² × 0.5, or approximately 14.137 cubic feet.

The combined volume is 78.137 cubic feet, approximately 2.894 cubic yards. The example button loads those two groups; the repeated rectangular beds are counted as a quantity of two. This is an illustrative quantity calculation, not a recommendation for the dimensions or soil depth of a particular planting.

When the soil volume becomes a weight

A bed’s dimensions cannot tell you the weight of the soil without its bulk density. Growing mixes and topsoil products can differ, and the moisture and packing condition matter. The weight option stays blank until you enter a density for your product.

As an arithmetic example, 2 cubic yards at a documented 2,000 lb/yd³ would weigh 4,000 pounds, or 2 US short tons. That example density is not a default for garden soil. Ask the supplier which density basis describes the delivered mix, and use our bulk density guide if the quote is unclear.

A geometric fill volume also differs from a supplier’s sale quantity. Loading increments, minimum orders or a product-specific settlement allowance may affect how much you buy. This calculator leaves those adjustments explicit instead of applying a universal percentage to every mix.

Measure once, avoid counting space twice

• Use inside dimensions. Wall thickness does not hold soil.
• For a top-up, measure the remaining gap at several representative points. One uniform depth is an approximation if the surface is uneven.
• Split an irregular bed into non-overlapping rectangles, or use a separate group for each independently measured round bed. Do not include paths between them.
• Measure the diameter of a round bed across its center. Entering the radius as a diameter would give one quarter of its actual area.
• Use separate plans if the groups will be filled with different products and you need a weight for each. The optional density applies to the whole combined plan.

This tool calculates quantity; it does not choose a soil recipe, assess drainage or determine whether a raised-bed structure can carry the load. For mulch over an existing layer, the mulch calculator has its own refill and bag-buying workflow. For a gravel surface, use the gravel coverage calculator.

Method and corrections

The calculator uses rectangular-prism and circular-cylinder geometry and the exact unit relationships of 27 cubic feet per cubic yard and 0.3048 meter per foot. Unit references: NIST conversion factors. Sources reviewed September 17, 2026.

The worksheet runs in your browser and saves no inputs. Browse all material tools, or send a correction to contact@cubicyardstotons.org.