Packaging Reference Library · Technical Reference

Film Gauge, Mil and Micron

How to convert plastic film thickness between gauge, mil, inch and micron, and why 'equivalent gauge' claims on high-performance stretch film must be tested, not converted.

Ref PK-0109ASTM D6988ASTM D4649ASTM D2103

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Plastic film thickness is quoted in several units. Gauge is used mainly for stretch film (100 gauge = 1 mil). Mil is one-thousandth of an inch and is common for poly bags and can liners. Micron (µm) is one-thousandth of a millimeter and is used internationally. ASTM D6988 covers how to measure film thickness. Some high-performance stretch films are sold by "equivalent" or "performance" gauge—a claim that a thinner film performs like a thicker conventional film—so the true gauge and the marketing gauge can differ.

How to identify

Stretch film boxes show gauge (e.g. 80 ga) and sometimes "true" or "equivalent" gauge; ask which.
Poly bags and liners show mil or micron.
Measure with a micrometer at several points; thin films are better measured by weight and area.

Conversion table

1 mil = 0.001 in = 100 gauge = 25.4 µm.

Gauge	Mil	Inch	Micron (µm)
50	0.5	0.0005	12.7
60	0.6	0.0006	15.2
70	0.7	0.0007	17.8
80	0.8	0.0008	20.3
90	0.9	0.0009	22.9
100	1.0	0.001	25.4
150	1.5	0.0015	38.1
200	2.0	0.002	50.8
300	3.0	0.003	76.2
400	4.0	0.004	101.6
600	6.0	0.006	152.4

Key points

Thickness alone does not define strength. Resin (LLDPE vs LDPE vs HDPE), layer structure and additives change puncture, tear and holding force.
HDPE liners are rated in microns and are much thinner than LLDPE liners of similar strength; do not compare across resins by thickness.
For stretch film, the useful comparisons are puncture, holding force and yield after pre-stretch (ASTM D4649 lists test methods).
When downgauging, run a trial on the actual loads and wrapper settings.

Common mistakes

Comparing an "equivalent 80 ga" film directly with an 80 ga true-gauge film on price per roll.
Confusing gauge with mil (a factor of 100).
Converting HDPE microns to LLDPE mils and assuming equal strength.

Governing standards: ASTM D6988; ASTM D4649; ASTM D2103.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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