How to read the chart
Find your bed’s inside size, then the depth of new material you are adding. Volume is length × width × depth. Bags are rounded up to whole bags, and nothing extra is added for settling or spillage: the soil calculator lets you choose an allowance and shows it separately.
For a top-up, use the depth of the missing layer, not the height of the frame. A 4 × 8 ft bed that has sunk 2 in needs 5.33 ft³ (4 bags of 1.5 ft³), not the 32 ft³ of a full 12 in fill.
Soil volume and bags by bed size and depth
| Bed and added depth | ft³ | yd³ | Litres | 1.5 ft³ bags | 2 ft³ bags | 50 L bags |
|---|---|---|---|---|---|---|
| 4 × 2 ft · 6 in | 4 | 0.148 | 113 | 3 | 2 | 3 |
| 4 × 2 ft · 8 in | 5.33 | 0.198 | 151 | 4 | 3 | 4 |
| 4 × 2 ft · 10 in | 6.67 | 0.247 | 189 | 5 | 4 | 4 |
| 4 × 2 ft · 12 in | 8 | 0.296 | 227 | 6 | 4 | 5 |
| 4 × 2 ft · 18 in | 12 | 0.444 | 340 | 8 | 6 | 7 |
| 4 × 4 ft · 6 in | 8 | 0.296 | 227 | 6 | 4 | 5 |
| 4 × 4 ft · 8 in | 10.67 | 0.395 | 302 | 8 | 6 | 7 |
| 4 × 4 ft · 10 in | 13.33 | 0.494 | 378 | 9 | 7 | 8 |
| 4 × 4 ft · 12 in | 16 | 0.593 | 453 | 11 | 8 | 10 |
| 4 × 4 ft · 18 in | 24 | 0.889 | 680 | 16 | 12 | 14 |
| 6 × 3 ft · 6 in | 9 | 0.333 | 255 | 6 | 5 | 6 |
| 6 × 3 ft · 8 in | 12 | 0.444 | 340 | 8 | 6 | 7 |
| 6 × 3 ft · 10 in | 15 | 0.556 | 425 | 10 | 8 | 9 |
| 6 × 3 ft · 12 in | 18 | 0.667 | 510 | 12 | 9 | 11 |
| 6 × 3 ft · 18 in | 27 | 1 | 765 | 18 | 14 | 16 |
| 8 × 4 ft · 6 in | 16 | 0.593 | 453 | 11 | 8 | 10 |
| 8 × 4 ft · 8 in | 21.33 | 0.79 | 604 | 15 | 11 | 13 |
| 8 × 4 ft · 10 in | 26.67 | 0.988 | 755 | 18 | 14 | 16 |
| 8 × 4 ft · 12 in | 32 | 1.185 | 906 | 22 | 16 | 19 |
| 8 × 4 ft · 18 in | 48 | 1.778 | 1,359 | 32 | 24 | 28 |
| 10 × 4 ft · 6 in | 20 | 0.741 | 566 | 14 | 10 | 12 |
| 10 × 4 ft · 8 in | 26.67 | 0.988 | 755 | 18 | 14 | 16 |
| 10 × 4 ft · 10 in | 33.33 | 1.235 | 944 | 23 | 17 | 19 |
| 10 × 4 ft · 12 in | 40 | 1.481 | 1,133 | 27 | 20 | 23 |
| 10 × 4 ft · 18 in | 60 | 2.222 | 1,699 | 40 | 30 | 34 |
| 12 × 4 ft · 6 in | 24 | 0.889 | 680 | 16 | 12 | 14 |
| 12 × 4 ft · 8 in | 32 | 1.185 | 906 | 22 | 16 | 19 |
| 12 × 4 ft · 10 in | 40 | 1.481 | 1,133 | 27 | 20 | 23 |
| 12 × 4 ft · 12 in | 48 | 1.778 | 1,359 | 32 | 24 | 28 |
| 12 × 4 ft · 18 in | 72 | 2.667 | 2,039 | 48 | 36 | 41 |
Combine beds before rounding
Round up once, for the whole order. Three 4 × 4 ft beds filled 8 in deep need 10.67 ft³ each. Rounded bed by bed, that is 24 bags of 1.5 ft³; added together first (32 ft³), it is 22. The saving is small, but it comes free with the right order of arithmetic. The calculator always combines beds before rounding.
Bags or bulk
Bulk material is usually sold by the cubic yard (27 ft³). Three 4 × 8 ft beds filled 12 in deep need 96 ft³, which is 3.56 yd³ or 64 bags of 1.5 ft³. At that scale, compare the price of bulk delivery with the bags, and ask the supplier whether their figure is loose or settled volume, and whether there is a minimum order.
What goes in the bed
This chart is about quantity only. The right mix depends on your native soil, your budget and what you grow. Your local Extension service publishes mix recommendations for your area; the guide to filling a raised bed covers measuring, and the methodology page lists the sources we use.