Raised Bed Soil Calculator
A raised bed soil calculator turns bed size into 1.5 cu ft bags: an 8 × 4 ft bed filled 10 in deep needs 18 bags, or $144 at $8 a bag.
What your order looks like
A few bags or one pickup trip will cover it.
0.99 yd³
7 wheelbarrow trips (4 cu ft each)
1 pickup load (2 cubic yards each)
Rules of thumb: A wheelbarrow trip of light material is 4 cubic feet. A pickup load of light material is 2 cubic yards.
Raised bed soil calculator formula
A raised bed soil calculator finds the volume of the bed and divides it by the size of one bag. The formula is bags = length × width × (depth in inches ÷ 12) ÷ 1.5, rounded up to a whole bag.
The 1.5 is the cubic feet in one bag of raised bed or garden soil. Bags come whole, so 17.78 bags means you buy 18. There is no waste box on this one. The rounding up gives you a small cushion, and the notes below cover settling.
Worked examples
Example 1 is the default bed, 8 ft × 4 ft filled 10 inches deep, at $8 per bag.
- Volume: 8 × 4 × (10 ÷ 12) = 26.67 cubic feet
- That is 0.988 cubic yards
- Bags: 26.67 ÷ 1.5 = 17.78, rounded up to 18
- Cost: 18 × $8 = $144
Example 2 is a bed 12 ft × 3 ft filled 11 inches deep.
- Volume: 12 × 3 × (11 ÷ 12) = 33 cubic feet
- Bags: 33 ÷ 1.5 = 22 exactly
- Cost: 22 × $8 = $176
The second bed lands on 22 bags with nothing left over. If you want a little spare for settling, buy 23.
Bags by bed size
At $8 per bag and 1.5 cubic feet per bag.
| Bed size | Fill depth | Cubic feet | Bags | Cost |
|---|---|---|---|---|
| 4 × 4 ft | 10 in | 13.33 | 9 | $72 |
| 3 × 6 ft | 10 in | 15.00 | 10 | $80 |
| 4 × 8 ft | 10 in | 26.67 | 18 | $144 |
| 4 × 8 ft | 12 in | 32.00 | 22 | $176 |
| 3 × 10 ft | 12 in | 30.00 | 20 | $160 |
| 4 × 12 ft | 12 in | 48.00 | 32 | $256 |
Eighteen bags make exactly one cubic yard. That is the point where bulk delivery starts to look better than hauling bags from the store.
Choosing how deep to fill
| Plants | Common fill depth |
|---|---|
| Lettuce, herbs, radishes | 6 to 8 inches |
| Most vegetables and flowers | 10 to 12 inches |
| Tomatoes, peppers, carrots | 12 inches or more |
These are rough rules of thumb. If your bed sits on bare soil and plants can root below the frame, you can fill less. If it sits on a patio or a liner, the whole root zone is the soil you put in, so fill to the depth the plant needs.
Some gardeners fill the bottom of a tall bed with logs, branches or other bulky organic material and put soil on top. That reduces the soil you need. Measure the depth of soil only, and enter that.
How to measure
- Measure inside the frame, not outside. A bed built from 2x lumber has about 3 inches less in each direction than the outside size.
- Measure the fill depth from the soil surface to the bottom of the bed, or to the top of any filler.
- Stop the fill a bit below the top. Leaving 1 to 2 inches of space helps keep water and soil in the bed.
- For an L-shaped or curved bed, divide it into rectangles and add the bags.
Common mistakes
- Using the outside dimensions of the frame. On a 4 × 8 ft bed built from 2x lumber, that overstates the volume by about 9 percent.
- Filling to the very top. Water and mulch need room.
- Ignoring settling. Compost-rich mixes drop within weeks, and you will see it.
- Buying different brands and mixing them blindly. Check that the bag size is 1.5 cu ft. Some bags are 1 cu ft or 2 cu ft, and the count changes with each.
- Using a mix with fertilizer your plants do not need. Read the label and follow it.
Related calculators
The garden soil calculator uses the same bag size with a shallower default. To add organic matter on top, see the compost calculator, and the topsoil calculator covers lawns and fill areas.
Frequently asked questions
What mix should I use to fill a raised bed?
A common approach is a blend of topsoil and compost, with something like peat moss, coco coir or perlite to keep it loose. Ratios vary by crop and by who you ask. Bagged raised bed mixes are pre-blended. This calculator counts the volume, so use it with whatever mix you choose.
Why 10 inches deep for a raised bed?
Ten inches is the calculator's default because it gives most vegetables and flowers room for roots. Root crops and tomatoes can want 12 inches or more, and lettuce and herbs can do with 6 to 8. Enter your own bed height.
Will the soil level drop after the first season?
Yes, loose, compost-rich soil settles and breaks down. Many gardeners top up a few inches each spring. The calculator has no waste option for this, so keep a few extra bags, or add a few inches of compost on top next year.
Is bulk soil cheaper than bagged for a raised bed?
Often, once you need more than about a cubic yard. This calculator assumes 1.5 cu ft bags, so 18 bags equal 27 cu ft, or one cubic yard. Compare your price for 18 bags with a local yard's price for a yard of the same mix, then add delivery.
How is this different from the garden soil calculator?
The math and the 1.5 cu ft bag size are the same. Only the starting depth differs, 10 inches here and 8 inches on the garden soil calculator. Enter your own depth in either and the result will match.
Estimates only. Verify quantities with your supplier before purchasing.