Bulk fill volume and soil-component bags
Base volume is the remaining space across identical beds. Order liters, cubic meters and cubic yards include the allowance, then split into your selected soil and compost shares. Each ingredient rounds separately to whole bags; surplus and cost use those whole counts.
Once the bed dimensions are set, the Plant Spacing Calculator counts rows and planting positions with edge clearance.
The formula
The compost percentage splits the adjusted volume; soil is the remainder. Dividing those two volumes by their respective bag sizes produces separate shopping quantities. The model does not infer a mix from the crop name. Bulk-unit equivalents include the same allowance as total order litres. Foot length converts with 0.3048 m/ft, inch depth with 2.54 cm/in, and each cubic-foot bag with 28.316846592 L/ft³. Circle area uses numerical pi. Other decimal inputs and whole-bag boundaries use exact fractions. Ingredient surplus is bag stock minus that component’s allowance-adjusted order.
Worked example
One 2 m by 1 m bed with 30 cm left to fill holds 600 L. A 10% order allowance raises this to 660 L. A 30% compost share gives 198 L compost and 462 L soil: five and twelve 40 L bags respectively. The 660 L order equals 0.660 m³ or approximately 0.863 yd³.
How to use this calculator
- Choose rectangle, circle or known liters per bed. For rectangles choose meters or feet; for circles enter the diameter in meters.
- Enter the remaining depth in centimeters or inches unless entering volume directly. Set identical-bed count, compost share and ordering allowance.
- Choose each ingredient’s liter or cubic-foot bag label independently. Optionally enter both bag prices in the same currency, then compare order, bags and surplus.
Inside dimensions and existing material
Measure the open interior and only the depth still needing material. Built-in reservoirs and existing fill reduce that space. Rectangle dimensions can use meters or feet; circle diameter uses meters. Known-volume entry accepts the remaining liters in one bed, which the whole bed count repeats.
Choosing a soil mixture
The compost share is adjustable because suitable mixtures depend on the existing soil, crop, drainage, and material quality. University extension guidance can help assess those conditions. This tool treats soil and compost as two volume components; it does not account for sand, aeration amendments, or chemical nutrient content. The allowance is extra material ordered relative to the empty volume, not a physical shrinkage model.
Round ingredient bags after the mix split
For a 600 L order split into 25% compost and 75% soil, the two components are 150 L and 450 L. With 40 L bags, buy four compost bags and twelve soil bags. Their excesses are 10 L and 30 L. At entered prices of 8 and 6 per bag, the combined material cost is 104 in that currency.
Package units are independent: a cubic-foot soil bag can be used beside a liter-labeled compost bag. Bulk equivalents describe the allowance-adjusted planned volume, while purchased bags can contain more. Delivery, taxes and supplier minimum orders are not included in the bag-price total.
Assumptions & limitations
What this calculation assumes
- Beds repeat the selected rectangular, circular or entered-volume shape and remaining fill.
- Ingredient proportions are measured by loose volume.
What to keep in mind
- Settlement and mixing can change final volume; no fixed shrinkage factor is prescribed.
Common questions
Can I use this for one premixed product?
Set compost to zero and use the soil bag field for the premixed product. All volume will be assigned to that component.
Does 30% compost mean 30% by weight?
No. It means 30% of the calculated loose volume. Materials with different densities will have different weight shares.
Does the cubic-yard result include extra allowance?
Yes. It converts the total order volume after allowance. If buying separate bulk components, multiply the total by each component’s fraction; whole-bag counts are a separate purchasing option.
Can I enter a volume I already measured?
Yes. Choose known volume per bed and enter the remaining liters for one bed. Bed count repeats that volume before allowance and component splitting.
Sources & further reading
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