Measure the space you will fill
Use the inside dimensions of each bed, not the outside frame. Enter the depth of soil you intend to add and the number of beds with those same dimensions. For different bed sizes, calculate each group separately and add the results.
Compare bagged and bulk soil
Read the cubic-foot volume on the bag. Bag sizes vary, so the 2-cubic-foot default is only an example. Bag counts round up; the bulk estimate retains the calculated volume. Enter both prices to compare the two purchasing methods. The same fixed delivery charge is applied to each comparison; adjust it if the quotes differ.
Formula and example
Cubic feet = inside length × inside width × depth in inches ÷ 12 × bed count × allowance factor. Divide by 27 for cubic yards, or by the bag volume and round up for bags. An 8 × 4-foot bed filled 12 inches deep needs 32 cubic feet before allowance. With 10% extra, that becomes 35.2 cubic feet, 1.30 cubic yards or 18 two-cubic-foot bags.
Choose the right fill
The tool measures space; it does not prescribe a soil blend. Subtract existing soil or other planned fill before entering the remaining depth. Allowance can account for settling or uneven surfaces, but actual needs depend on the selected product.