Enter the inside length, width and depth of the bed and the number of beds of that size. The calculator works out the soil volume in cubic feet and cubic yards and how many bags of the size you pick fill them.
How the raised bed soil calculator works
- Volume = length × width × depth × number of beds. Depth in inches is divided by 12 to get feet.
- Cubic yards = cubic feet ÷ 27.
- Bags = cubic feet ÷ bag size, rounded up.
This is the method the University of Florida IFAS Extension uses in its raised bed guide. Its example, a 4 × 8 ft bed 21¾ in deep, needs about 2.15 cubic yards. The guide also says to fill to the top of the bed because the soil level may drop about 2 in as it settles, and to top it off each season.
Soil for common bed sizes
| Bed (inside) | Cubic feet | Cubic yards | 1.5 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft, 12 in deep | 16 | 0.59 | 11 | 8 |
| 8 × 4 ft, 12 in deep | 32 | 1.19 | 22 | 16 |
| 8 × 4 ft, 18 in deep | 48 | 1.78 | 32 | 24 |
| 10 × 4 ft, 12 in deep | 40 | 1.48 | 27 | 20 |
| 8 × 4 ft, 24 in deep | 64 | 2.37 | 43 | 32 |
Worked example
Three 8 × 4 ft beds, each 12 in deep, hold 8 × 4 × 1 × 3 = 96 cu ft of soil, or 3.56 cubic yards. In 2 cu ft bags that is 48 bags. At this size, bulk soil delivered by the yard is usually cheaper than bags.
Filling a raised bed
- Measure the inside of the bed; thick boards or blocks make it smaller than the outside size.
- Raised bed mixes usually blend topsoil with compost and other organic matter. Your local extension office can suggest a mix for your area.
- If the bed sits on lawn, you can lay cardboard first instead of digging out the grass.
- Plan to top up the beds with compost each season as the soil settles.
Step by step: filling raised beds
Tips before you buy
- Bag sizes are usually printed in cubic feet or quarts; 1 cu ft is about 25.7 dry quarts.
- Ask the supplier what is in a bulk mix and whether it has been screened.
- The mulch calculator estimates mulch for paths and beds.
- See the mulch depth guide for how thick to spread it.
