Gauge to Micron Conversion Chart

If you order polythene regularly, you will come across two different ways of describing how thick it is: gauge and microns. The two systems measure the same thing but use different scales, and mixing them up can lead you to order material that is too thin for the job or pay over the odds for strength you do not need.

This guide explains what gauge and microns actually measure, gives you a full conversion chart, and helps you work out which thickness suits your application.

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These figures give you a reliable starting point, but always check the exact specification on your order confirmation. Manufacturing tolerances mean actual thickness can vary slightly between suppliers and production runs.

What Is Gauge?

Gauge is the traditional imperial measurement used across the UK polythene industry. It's a unitless number, so you won't see "mm" or "microns" attached to it. As a rule, the higher the gauge number, the thicker and stronger the film.

Gauge measurements can look large at first glance. A gauge of 500 sounds substantial, but it actually describes a film that's only half a millimetre thick.

What Is a Micron?

A micron (also written as µm or "mu") is a metric unit equal to one thousandth of a millimetre. Microns give you a more precise, internationally recognised way to specify film thickness, which is why many manufacturers and specifications now quote thickness in microns rather than gauge.

To put the scale in perspective, a standard sheet of A4 paper is roughly 100 microns thick. A single human hair measures around 70 to 100 microns in diameter. Polythene film for everyday use typically ranges from around 20 microns for the lightest films up to 300 microns or more for heavy-duty applications.

 How To Convert Gauge to Microns

The conversion is straightforward once you know the formula: 

• To convert gauge to microns, divide the gauge figure by 3.937 (commonly rounded to 4).
• To convert microns to gauge, multiply the micron figure by 3.937 (commonly rounded to 4).
• To convert microns to millimetres, divide the micron figure by 1000.

So a 100 gauge film works out to roughly 25 microns, or 0.025mm. A 500 gauge film comes to around 125 microns, or 0.125mm.

Most suppliers round the conversion factor to 4 for everyday use, since it's simpler to calculate and the difference is negligible for practical purposes. If you need a precise figure for a technical specification, use 3.937 instead.

Why the Right Thickness Matters

Choosing the correct gauge or micron isn't just about cost. Get it wrong, and you risk splits, tears, and punctures, which means damaged goods, wasted material, and unhappy customers. Order too thick, and you pay for strength you don't need, while using more material than the job requires. 

• Weight of the Contents: Heavier loads need a higher gauge to resist stretching and tearing. A 500 gauge rubble sack, for example, can typically carry loads of up to 40kg, while lighter gauges are only suitable for lighter waste.
• Handling & Transport: Film that gets dragged, stacked, or moved repeatedly needs more resilience than film used once and disposed of.
• Storage Conditions: Outdoor or long-term storage exposes film to UV light, which breaks down standard polythene and makes it brittle over time. Rather than simply going thicker, the more effective solution is UV-stabilised film, which is treated to resist this breakdown regardless of gauge.
• Regulatory Requirements: Some applications carry a specified minimum thickness.

Need Help Choosing the Right Thickness?

At Polythene UK, we help customers match the right thickness to the job, so you get the protection you need without paying for material you don't. We also offer lightweight, high-performance alternatives such as our Polylite range, which can maintain strength at a lower gauge, cutting material use and cost without compromising on protection.

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