Raised Bed Soil Calculator — Mix by Recipe
Find out exactly how much soil your raised beds need — and how to split it by recipe. Enter your bed size and pick a mix; the calculator breaks the total into compost, peat, and other components with bag counts.
How to use this calculator
- Enter the length, width, and soil depth of one bed, and how many identical beds you have.
- Choose a recipe. Mel’s Mix (equal thirds of compost, peat or coir, and vermiculite) is the classic Square Foot Gardening blend.
- Pick your bag size; the calculator splits the total and gives a bag count per component.
- Buy a little extra — soil settles and compacts after the first watering.
The formula
Total volume = length × width × depth (in) ÷ 12 × number of beds, giving cubic feet.
Each recipe component is a fraction of that total. Mel’s Mix is three equal thirds; a 50/50 blend is two halves.
Bags per component = component cubic feet ÷ bag size, rounded up.
Worked example
One 8 ft × 4 ft bed, 10 in deep, Mel's Mix, 1.5 cu ft bags.
Volume = 8 × 4 × (10 ÷ 12) = 26.7 cubic feetEach third = 8.9 cubic feetBags per component = 8.9 ÷ 1.5 = 5.9 → 6 bags each
An 8×4 bed needs about 26.7 cu ft — roughly 6 bags each of compost, peat, and vermiculite.
Frequently asked questions
How many bags of soil for a 4x8 raised bed?
A 4×8 bed at 10 inches deep holds about 26.7 cubic feet. That is roughly 18 bags of 1.5 cu ft soil for a single fill, or about 6 bags each of three components for Mel’s Mix.
What is Mel's Mix?
Mel’s Mix, from Square Foot Gardening, is equal parts by volume of compost (ideally blended from several sources), peat moss or coconut coir, and coarse vermiculite. It drains well and needs little added fertilizer.
How deep should a raised bed be?
Six to twelve inches works for most vegetables. Go deeper (12 inches or more) for carrots, potatoes, and other root crops, or if the bed sits on a hard surface rather than open ground.