Raised beds are usually filled with a soil mix, bought in bags of 1.5 cu ft or as bulk mix sold by the cubic yard, where a cubic yard is 27 cubic feet. Bulk mix suits a row of beds filled at the same time, and bags suit a small project or a top-up. Depth is the input that depends most on the crop you grow, so the next section covers it first.
How to use this calculator
- Choose the shape of the bed. Rectangle fits most raised beds, and circle suits a round bed.
- Measure inside the boards, in feet. The boards take up no soil, so measuring the outside overstates the volume.
- Set the soil depth for the crops you plan to grow. The depth section lists the range, from shallow greens to deep-rooted plants.
- If you are building several identical beds, enter the count in quantity. The total covers all of them, so the order covers the whole row.
- Choose how you will buy: bags for a few beds, or cubic yards of bulk mix for more. Round up when you shop, because a short load leaves a bed partly empty.
Worked examples
Salad greens bed
8 ft × 4 ft, 8 in deep
- cubic yards
- 0.79
- cubic feet
- 21.33
- bags of 1.5 cu ft
- 15
Tomato and pepper bed
8 ft × 4 ft, 12 in deep
- cubic yards
- 1.19
- cubic feet
- 32
- bags of 1.5 cu ft
- 22
Row of matching beds
4 × 8 ft × 4 ft, 12 in deep
- cubic yards
- 4.74
- cubic feet
- 128
- bags of 1.5 cu ft
- 86
Round herb bed
4 ft diameter, 8 in deep
- cubic yards
- 0.31
- cubic feet
- 8.38
- bags of 1.5 cu ft
- 6
Cubic yards of soil for common raised bed sizes
| Area | 8 in deep | 12 in deep | 24 in deep |
|---|---|---|---|
| 4 × 4 ft | 0.395 | 0.593 | 1.19 |
| 4 × 8 ft | 0.79 | 1.19 | 2.37 |
| 4 × 12 ft | 1.19 | 1.78 | 3.56 |
| 3 × 6 ft | 0.444 | 0.667 | 1.33 |
Cubic yards, exact volume without extra for waste.
Depth by crop
Leafy greens, beans and cucumbers do well in the shallow end of the range, with at least 8 inches of soil. Peppers, tomatoes and squash need more room for their roots, and the calculator's starting value of 12 inches suits those deep-rooted crops. At that depth, a cubic yard covers 27 square feet of bed.
Across all crops, the useful range runs from 8 to 24 inches. A deeper bed holds more soil, so match the depth to the plants rather than to the height of the frame you built.
Bags or a bulk mix?
Bags are simplest for a small bed or a top-up. A cubic yard takes 18 bags of 1.5 cu ft, and each bag is carried, cut open and emptied by hand, so a long bag count means many trips.
A bulk mix suits several beds filled at the same time. Ask whether the product is sold as a raised-bed mix or as plain topsoil, because the two behave differently once they are packed into a closed frame.
Filling a very deep bed
A very deep bed does not have to be filled with planting mix all the way down. Many gardeners put coarser material in the lower part and cap it with the mix, so the soil you buy only needs to cover the top layer.
Enter the depth of the planting layer rather than the full depth of the frame, so the calculator matches what you actually buy. Keep that top layer deep enough for the crops, and check that the lower material drains freely.
Mistakes to avoid
- Measuring the outside of the frame. Measure inside the boards instead.
- Leaving out the quantity. Several identical beds multiply the total, so enter the count.
- Ignoring settling. Fill a little above the rim, and top up after the soil has settled.
- Buying for the frame rather than the crop. Match the depth to the roots you plan to grow.
How do I calculate how much soil I need for a raised bed by hand?
Measure the inside length, width and depth in feet. To turn inches of depth into feet, divide by 12 inches. Multiply the three numbers to get cubic feet. Divide by 27 cubic feet for cubic yards of bulk mix, or by 1.5 cu ft for the number of bags, and round up.
Common questions
How many bags of soil do I need for a standard raised bed?
Work out the bed's volume in cubic feet, divide by the size of one bag and round up. The calculator does that for each bed, and for the total when you enter a quantity. A common bagged size is 1.5 cu ft, and a cubic yard takes 18 of them.
How many bags of soil make a cubic yard?
With bags of 1.5 cu ft, a cubic yard takes 18 bags. Some bags are labeled by weight, and weight does not tell you the volume, so look for the cubic feet on the label.
How deep should a raised bed be?
It depends on the crop. A bed at least 8 inches deep suits leafy greens, beans and cucumbers, while deep-rooted plants need more, with the full range running from 8 to 24 inches.
Does soil settle after I fill a raised bed?
Yes. Loose soil sinks once it is watered and rained on, so the surface gradually drops. Fill a little above the rim, and rake the top level once it has settled.
How much extra soil should I buy for a raised bed?
Soil sinks after watering, so it helps to order a little more than the exact volume. A common starting point is 15 percent extra, which you can raise or lower to suit your soil. Round up to whole bags or the next load size.
How do I convert raised bed soil volume to liters or cubic meters?
One cubic foot is 28.317 liters, and one cubic yard is 0.765 cubic meter. Multiply your bed's volume by the matching value to switch units.
What is the ideal soil mix or ratio for a raised garden bed?
A common extension recipe is about 70 percent topsoil and 30 percent compost. Another is equal parts topsoil, compost and coarse sand. Either way, aim for organic matter of 25 to 50 percent of the mix by volume.