FIBC bag calculation: volume, fill weight and bags per batch

The purchasing question

A big bag calculation can mean several different questions: the internal filled volume, estimated product mass, the number of bags needed for a batch or packaging cost per tonne. Keep these quantities separate. A dimensional estimate helps plan space but does not approve a payload or establish the strength of the bag.

Calculation method

Calculate rectangular volume as internal length × width × filling height in meters. Estimated product mass is volume × (1 − volume headspace fraction) × measured bulk density. Select the approved planned fill separately, then calculate filled bags as ceil(batch kilograms ÷ planned fill kilograms). Purchase quantity includes any deliberate spare bags.

Worked example

A 900 × 900 × 1,200 mm fill is 0.972 m³. At 800 kg/m³ and 10% headspace it implies 699.84 kg of product. If an independently approved plan uses 650 kg per bag, a 15,000 kg batch requires 24 filled bags. The last carries 50 kg. Two spares bring the purchase to 26 bags.

At €8 per bag, €1 per separate liner and €50 empty-packaging freight, 26 purchased bag-and-liner sets cost €284. Divide by 15 tonnes for €18.9333 per batch tonne. This purchase allocation includes spares and freight; the FIBC component cost per tonne calculator uses a different cost boundary and need not give the same answer.

Checks before using the result

• Use internal filled dimensions, excluding loops and spouts.
• Use actual product bulk density, not solid material density.
• Confirm the approved planned fill against the supplier specification.
• Distinguish purchase freight for empty bags from freight for packed product.

Common questions