Raised Bed Soil Calculator
Calculate how many bags of soil mix you need to fill a raised garden bed at your depth, plus total cost at your price per bag.
How this calculator works
Filling a raised bed usually means combining topsoil, compost, and an aeration amendment rather than a single bagged product, but the volume math is the same. This calculator converts your bed’s dimensions and fill depth into cubic yards, then divides by the standard 1.5 cubic foot bag size to give you a bag count for that blended mix.
Formula: Cubic yards = (Length ft × Width ft × Depth ft) ÷ 27. Bags = (Cubic yards × 27) ÷ 1.5.
Worked example
An 8 ft × 4 ft raised bed at a 10-inch fill depth:
- Depth in feet: 10 ÷ 12 ≈ 0.8333 ft
- Cubic yards: (8 × 4 × 0.8333) ÷ 27 ≈ 0.9877 yd³
- Bags: (0.9877 × 27) ÷ 1.5 ≈ 17.78 bags
- At $8/bag, that’s $142.22.
Coverage reference
| Bed size | Bags needed (10 in) |
|---|---|
| 4 × 2 ft | 4.44 bags |
| 8 × 4 ft | 17.78 bags |
| 16 × 8 ft | 71.11 bags |
How to measure your bed
Measure the inside length and width of your raised bed frame, not the outer dimensions, and fill depth to the level you plan to plant at, typically 10-12 inches for a standard bed. If you’re mixing your own 60/30/10 recipe rather than buying a premixed bagged blend, apply this calculator’s bag total across your three components proportionally.
Frequently asked questions
What mix should I use to fill a raised bed?
A widely used starting recipe is roughly 60% topsoil, 30% compost, and 10% aeration material like perlite, vermiculite, or coarse sand. That blend gives you nutrient-rich soil with enough drainage and looseness for vegetable roots to spread easily, which is a different goal than the bagged garden soil calculator's single-product estimate.
Why 10 inches deep for a raised bed?
Most vegetables root effectively in the top 10-12 inches of soil, and that's deep enough for root crops like carrots while still being a manageable fill volume. Shallow beds under 6 inches limit root development and dry out faster in hot weather.
Will the soil level drop after the first season?
Yes — fresh bed mix, especially one heavy in compost, settles noticeably as organic matter breaks down and the loose fill compacts from watering. Plan to top off a new raised bed with an extra bag or two of compost or mix each spring for the first couple of years.
Is bulk soil cheaper than bagged for a raised bed?
For a single small bed, bagged mix is usually more practical since most delivery minimums are 1+ cubic yards. Once you're filling several beds or a bed larger than this calculator's 8 × 4 ft default, a bulk delivery of blended garden soil often works out cheaper per cubic yard — check the cubic yard calculator to convert your total bag count.
How is this different from the garden soil calculator?
The garden soil calculator estimates a single bagged product straight from the bag's cubic footage. This calculator is framed around the classic raised-bed recipe and depth, making it the better starting point specifically for filling a new vegetable bed frame.
Estimates only. Verify quantities with your supplier before purchasing.