MEASURING GUIDE
How to measure a raised bed for soil
Use the space the soil will occupy, rather than the outside dimensions of the frame.
Measure inside the walls
Measure the inside length and inside width. Outside dimensions include the thickness of the frame and can overstate the fill volume. For an irregular bed, divide the space into non-overlapping rectangles and calculate each one separately.
Enter the depth left to fill
The fill depth is the distance from the current surface to the soil level you want. If a 12 in high bed already contains 6 in of material, enter only the remaining 6 in. Account for any space you want below the top rim. The calculator does not decide the appropriate growing depth for a plant.
A 4 × 8 ft example
A bed with inside dimensions of 4 × 8 ft and 12 in to fill needs 32 cubic feet. That is about 1.19 cubic yards, or 16 bags at 2 cu ft per bag. If only 6 in remains, the volume is 16 cubic feet and you need 8 of those bags, before any extra allowance.
Keep volume and soil choice separate
Soil composition, existing ground, drainage and the plants you grow affect material choice. Settling varies with material and conditions. Our base calculation adds no automatic settling allowance; you can enter an allowance explicitly after checking your situation.
Read University of Maryland Extension: Soil to Fill Raised Beds for different starting conditions. The calculator estimates volume; it does not prescribe one universal soil blend.