What is Gauge? Micron, Mil and Gauge Explained
Gauge is a general word for the thickness of plastic film. Australia quotes film thickness in microns. The United States uses mil, meaning thousandths of an inch, and gauge, where 100 gauge equals 1 mil. One mil is 25.4 microns, so one gauge is 0.254 microns.
The three units and where you will meet each one
Micron is the Australian unit, written µm. It is one thousandth of a millimetre, and our guide to what a µm is covers the unit itself in full. Every film spec in this country is quoted in microns, and so is most of Europe and Asia.
Mil is one thousandth of an inch. It is the standard unit on American spec sheets and it is the single biggest trap in imported packaging documents, because mil looks like an abbreviation for millimetre and is nothing of the sort. A 2 mil bag is not 2mm thick. It is 50.8 microns, or about a twentieth of a millimetre.
Gauge in the American sense is simply mil multiplied by 100, so 100 gauge is 1 mil and 80 gauge is 0.8 mil. It exists because film thicknesses are small and awkward numbers in mil, and multiplying by 100 gives whole numbers that are easier to say on a warehouse floor.
There is a second, looser Australian use of the word. When somebody here asks what gauge a stretch film or a bin liner is, they usually mean what micron is it. Gauge in that sentence just means thickness. It is worth checking which one a supplier means before you order, especially if any part of the supply chain is offshore.
Shop plastic film by thickness
From 20 micron pallet wrap through to 200 micron builders film, all quoted in microns.
Stretch Wrap
The thin end of the scale: 20, 23 and 25 micron pallet wrap.
Shop stretch wrap
Plastic Poly Bags
LDPE poly bags from 35 micron up to heavy duty 150 micron.
Shop poly bags
Layflat Tubing
LDPE tube in 50, 100 and 150 micron, sold by roll weight.
Shop layflat tubing
Builders Film Roll
The heavy end: 100 micron and 200 micron centrefold site film.
Shop builders filmMicron to mil to gauge conversion table
All conversions below are worked from 1 mil = 25.4 microns and 100 gauge = 1 mil. Figures are rounded and are approximate.
| Micron | Mil (approx) | Gauge (approx) |
|---|---|---|
| 20µm | 0.79 | 79 |
| 25µm | 0.98 | 98 |
| 30µm | 1.18 | 118 |
| 35µm | 1.38 | 138 |
| 50µm | 1.97 | 197 |
| 75µm | 2.95 | 295 |
| 100µm | 3.94 | 394 |
| 150µm | 5.91 | 591 |
| 200µm | 7.87 | 787 |
The three sums you need are short. To go from mil to microns, multiply by 25.4. To go from microns to mil, divide by 25.4. To go from mil to gauge, multiply by 100. So a US film quoted at 80 gauge is 0.8 mil, which is 20.32 microns, near enough to the 20 micron pallet wrap sold here.
What each Australian thickness is used for
| Micron | Typical Australian use |
|---|---|
| 20 to 25µm | Hand and machine stretch pallet wrap |
| 30 to 35µm | Light poly bags, produce and garment bags, the bag ban threshold |
| 50µm | General purpose poly bags, standard resealable bags, layflat tubing |
| 75µm | Heavy duty resealable bags, parts and hardware packing |
| 100µm | Heavy duty poly bags, layflat tubing, lighter site film |
| 150µm | Industrial bags and tubing where puncture risk is high |
| 200µm | Heavy builders film for site protection and covering |
Why thicker is not automatically stronger
Thickness is one variable, not the whole story. The resin matters more than most buyers expect. LLDPE stretches and absorbs a shock where LDPE of the same thickness tears, which is why 25 micron stretch film can hold a pallet together and a 25 micron bag would split. Construction matters too: a blend, a co-extruded film or an added cling layer all change how a film behaves under load. Puncture resistance, tear resistance and stretch are separate properties, and a heavier film that is the wrong type will still fail. Choose the film first, then the thickness.
Why a stated thickness is a nominal figure
Film thickness is measured with a micrometer, usually at several points across the web, and the number on the label is a nominal figure with a manufacturing tolerance around it. A 50 micron bag will not measure exactly 50.0 microns everywhere. Extrusion is a continuous process and a small variation across the width of the film is normal and expected. Some products are not sold by thickness at all: layflat tubing is commonly supplied by roll weight in Australia, in 10kg and 15kg rolls, so the metres you get on a roll depend on both the width and the micron. If you are comparing quotes, check you are comparing the same thickness, the same width and the same quantity basis.
Australian context: the 35 micron line and imported specs
One number turns up more than any other in Australian packaging, and that is 35 microns. NSW, Victoria, Tasmania and Queensland all ban lightweight plastic shopping bags with handles at or under 35 microns. Queensland goes further and requires a compliant bag to be 35 microns or thicker, to carry at least 80% verified recycled content and to hold 10kg for at least 125 uses. Western Australia bans all plastic shopping bags with handles regardless of thickness, South Australia bans all plastic film shopping bags that are not AS-certified compostable, and the ACT has banned lightweight bags under 35 microns as well as heavyweight boutique bags over 35 microns. The Northern Territory bans lightweight checkout-style bags without publishing a micron figure. That single threshold is why so many Australian bag specs sit at exactly 35 microns.
It also explains why the conversion matters. 35 microns is roughly 1.38 mil or 138 gauge, which is not a round number in either American unit and never appears on a US spec sheet. If a supplier overseas offers you a bag at 1.5 mil, that is about 38 microns, and if they offer 1.25 mil, that is about 32 microns and would fall on the wrong side of the line in four states. Convert before you commit, not after the container lands.
Popular film at each thickness
Every product below is quoted in microns. Despatched from Brisbane, same day on stock orders before 12pm.
Related guides
For the micron itself, start with What is a µm (um)?, which explains the unit and how to choose a thickness for a given job. Then see What is LDPE? and What is LLDPE? for the two resins whose behaviour at a given thickness differs the most.
What is stretch wrap? covers the 20 to 25 micron end in detail, including how gauge choice affects containment force. To buy by thickness, browse our poly bags and layflat tubing.
Working from an imported spec sheet and not sure what it converts to? Contact our Brisbane team on 1800 555 343.
