Multiply the internal length by internal width and fill depth, then multiply by the number of beds. Deduct any existing fill and add a reasonable allowance for settling.
Garden bed planning tool
Raised Bed Soil Calculator
Calculate soil for one or several raised beds, convert the result into bags or bulk volume, and split the fill into a custom soil blend.
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Plan your raised-bed fill
Measure the inside space that will actually be filled.
Estimated result
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Enter the project details and calculate.
Raised-bed method
Calculate the empty space that will actually be filled
A raised bed is a three-dimensional container. The useful measurement is the internal length × internal width × fill depth, multiplied by the number of identical beds.
Measure inside the frame
Timber, blocks and corrugated panels occupy space. Measuring the outside can overstate the soil requirement, especially in small beds with thick walls. Measure the open planting area and the actual unfilled depth.
Deduct existing material
If the bed already contains soil, logs, rubble or a drainage layer, calculate only the remaining void. A twelve-inch frame does not require twelve inches of new mix when six inches are already filled.
Allow for settling
Fresh loose material settles after watering and cultivation. The allowance gives a planning buffer, but it should not be treated as a universal compaction factor.
Blend planning
Use the ratio as a volume split, not a soil prescription
The calculator separates the total fill into topsoil, compost and an aeration component. It does not claim that one recipe suits every crop or climate.
How the ratio works
A 6:3:1 ratio contains ten total parts. Six-tenths of the required volume is topsoil, three-tenths compost and one-tenth aeration material.
Total volume × component parts ÷ all partsChange the parts to match advice from a local soil test, horticultural supplier or crop guide.Worked example
Two 8 × 4 ft beds filled 12 inches deep
The unadjusted volume is 64 cubic feet, or about 2.37 cubic yards. With 10% extra, the requirement becomes roughly 2.61 cubic yards before supplier rounding.
Buying implication: bagged soil can be practical for one shallow bed, but multiple deep beds often make bulk delivery easier. Compare the bag count against a local bulk quote before ordering.
Frequently asked questions
Raised-bed soil calculator questions
Not necessarily. Many beds use a blend of mineral soil, compost and other materials. The correct mix depends on drainage, crop requirements and local soil quality.
No. Measure the open internal space because the frame material does not need soil.
A modest buffer can cover settlement and measurement differences, but the right percentage depends on material condition and project certainty.