Microns versus GSM: why equal thickness does not mean equal weight

The purchasing question

Thickness describes the distance through a film; GSM describes the mass covering one square metre. Purchasing a thinner film does not necessarily reduce the price per useful pack if its composition or required production layout changes. Keep both properties in a supplier comparison, especially when the quotations come from different material structures.

Calculation method

For a uniform material, GSM = thickness in micrometres × density in g/cm³. The inverse is thickness = GSM ÷ density. Enter the density appropriate to the actual material rather than borrowing one from a different film. For a laminate, calculate layers separately or use measured total GSM.

Worked example

With an illustrative density of 0.92 g/cm³, 50 µm implies 46 GSM. A second hypothetical material at 1.20 g/cm³ and the same 50 µm implies 60 GSM. A 10,000 m² order therefore contains 460 kg or 600 kg respectively. Equal thickness produces different order mass.

These figures compare mass, not barrier performance, sealing behaviour or strength. An equivalent packaging specification needs separate technical confirmation. Use a representative supplier-measured GSM where available and retain the dimensional estimate as a cross-check.

Checks before using the result

• Confirm that thickness is in µm, not mm.
• Use the full structure GSM for a multilayer web.
• Do not treat illustrative density as a guaranteed material property.

Common questions