Soil & Raised Beds
Raised Garden Bed Soil Calculator: How Much Soil Do I Need?
Work out how much soil you need to fill a raised garden bed. Enter the bed size and depth to get litres, cubic metres, and the number of bags.
Estimated soil needed
Raised bed soil results
For 1 rectangular bed measuring 4 ft by 8 ft at 12 in deep, you need 32 cubic feet of soil before extra allowance.
How to use this calculator
Choose the bed shape, enter the bed dimensions, select your unit system, and add the number of beds. If you want a buffer for settling or uneven fill, choose 5%, 10%, or 15% extra. Select a bag size to estimate soil bags for raised garden bed planning.
Formula used
The calculator uses a simple volume formula:
volume = length x width x depth x number of beds
For imperial inputs, length and width are entered in feet and soil depth is entered in inches. The depth is converted to feet before calculating volume. For metric inputs, length and width are entered in metres and depth is entered in centimetres, then converted to cubic feet, cubic yards, and litres.
Example: 4x8 raised bed, 12 inches deep
A 4x8 raised bed that is 12 inches deep needs 4 x 8 x 1 = 32 cubic feet of soil. That equals about 1.19 cubic yards or 906 litres. With a 10% extra allowance, the recommended order amount is 35.2 cubic feet. If you buy 1.5 cubic foot bags, round up to 24 bags.
Common raised bed sizes table
| Bed size | Depth | Soil needed | Bulk equivalent |
|---|---|---|---|
| 2 ft x 4 ft | 12 in | 8 cu ft | 0.30 cu yd |
| 3 ft x 6 ft | 12 in | 18 cu ft | 0.67 cu yd |
| 4 ft x 4 ft | 12 in | 16 cu ft | 0.59 cu yd |
| 4 ft x 8 ft | 12 in | 32 cu ft | 1.19 cu yd |
| 4 ft x 10 ft | 12 in | 40 cu ft | 1.48 cu yd |
How much extra soil should you buy?
Most raised beds settle after watering, especially when the mix contains compost, peat, coir, or loose organic matter. A 5% buffer is reasonable for small beds with accurate measurements. A 10% buffer is a practical default for new raised beds. Use 15% if the ground is uneven, the bed is deep, or you are filling several beds at once.
Soil depth guide by plant type
| Plant type | Typical soil depth | Notes |
|---|---|---|
| Leafy greens and herbs | 6 to 8 in | Works for lettuce, spinach, basil, and many shallow-rooted crops. |
| Beans, peppers, and flowers | 8 to 12 in | A good range for many common garden plants. |
| Tomatoes and cucumbers | 12 to 18 in | More depth supports larger root systems and steadier moisture. |
| Carrots and root crops | 12 in or more | Loose, deep soil helps roots size up cleanly. |
Common mistakes
- Using inches for depth without converting to feet in the final raised bed soil calculator cubic feet formula.
- Forgetting to multiply by the number of beds.
- Buying exactly the calculated amount with no allowance for settling.
- Confusing bag volume with bag weight. Soil bags are often sold by cubic feet or litres, not only pounds.
- Assuming every bed is perfectly level or perfectly rectangular.
FAQ
Raised bed soil calculator FAQ
How much soil do I need for a raised bed?
Multiply length by width by soil depth, then multiply by the number of beds. This gives volume before adding any extra allowance.
How much soil does a 4x8 raised bed need at 12 inches deep?
A 4x8 raised bed at 12 inches deep needs 32 cubic feet, about 1.19 cubic yards, or about 906 litres of soil.
How many bags of soil are needed for a 4x8 raised bed?
At 12 inches deep with 10% extra, a 4x8 bed needs 35.2 cubic feet. That is 36 one-cubic-foot bags, 24 bags at 1.5 cubic feet, or 18 bags at 2 cubic feet.
What is the difference between cubic feet and cubic yards?
Cubic feet is common for bagged soil. Cubic yards is common for bulk soil. One cubic yard equals 27 cubic feet.
Can I calculate multiple raised beds at once?
Yes. Enter the dimensions for one bed, then set the number of beds. The calculator multiplies the volume by that count.
What if my raised bed is square?
Select square and enter the side length. The calculator uses the same value for length and width.
Is 40 L the same as cubic feet?
No. A 40 liter bag is about 1.41 cubic feet. The calculator converts 40 L bags before estimating bag count.
Should I fill a raised bed completely to the top?
Usually leave a little space below the rim so water, mulch, and soil do not spill out. Soil may also settle after the first few waterings.