Raised Garden Bed Calculator
Work out how much soil, and which mix of ingredients, to fill one or more raised garden beds.
How to use this raised bed calculator
Enter how many beds you're filling and the inside length and width of one bed in feet. For depth, use how deep the soil will be, usually the bed's height minus an inch or two at the top. Pick a soil mix and the bag size you're buying, and the calculator splits the total into each ingredient.
- 60/40 topsoil and compost: affordable and holds up well, and the easiest to buy in bulk.
- Thirds mix (compost, peat moss or coconut coir, vermiculite): very light and fluffy, popular for square-foot gardening, but costs more.
- Bagged raised-bed mix: the simplest option, ready to use straight from the bag.
How deep should a raised bed be?
| Crops | Soil depth |
|---|---|
| Lettuce, herbs, strawberries | 6 to 8 in |
| Most vegetables (peppers, beans, kale) | 10 to 12 in |
| Tomatoes, carrots, potatoes | 12 to 18 in |
The math behind it
Cubic feet = number of beds × length × width × (depth ÷ 12). Each ingredient is that total times its share of the mix, and bags = cubic feet ÷ bag size, rounded up.
Example: two 8 × 4 ft beds filled 12 inches deep hold 64 cubic feet (about 2.4 cubic yards). With the 60/40 mix that's 38.4 cu ft of topsoil and 25.6 cu ft of compost, or 26 and 18 bags of 1.5 cu ft.
Often used together
Quick answers
How much soil do I need for a 4 × 8 raised bed?
At 12 inches deep, 32 cubic feet: about 22 bags of 1.5 cu ft or 1.2 cubic yards. At 6 inches, half that.
Is it cheaper to buy soil in bulk or in bags?
For more than about 1 cubic yard (27 cu ft), bulk delivery is usually cheaper, even with the delivery fee. For one or two small beds, bags are easier.
Should I put anything at the bottom of a raised bed?
Cardboard works well to smother grass and weeds underneath. Skip gravel at the bottom: it doesn't help drainage and actually holds water in the soil above it.