To convert microns to mil, divide by 25.4. To convert microns to UK gauge, divide by 0.254 (or multiply by about 3.937). One mil equals 25.4 µm and 100 gauge, so a film quoted as 2.5 mil, 250 gauge or 63.5 µm is the same thickness. The converter below turns any one of the three units into the other two, and the tables underneath list the common values if you prefer to look them up.
This page only converts units. For how thickness relates to bag strength, handle style and load, read plastic bag thickness explained.
How do you convert microns, gauge and mil?
Use these exact relationships. Micron means micrometre (µm), one thousandth of a millimetre. A mil is one thousandth of an inch, and an inch is 25.4 mm.
- Mil from microns: mil = µm ÷ 25.4
- Microns from mil: µm = mil × 25.4
- UK gauge from microns: gauge = µm ÷ 0.254, which is the same as µm × 3.937
- Microns from UK gauge: µm = gauge × 0.254
- Gauge from mil: gauge = mil × 100
For a quick estimate, gauge is roughly four times the micron figure. The exact factor is 3.937, so 50 µm is 197 gauge rather than 200.
What does "gauge" mean on a polythene quote?
In the UK polythene and film trade, 100 gauge equals 1 mil, which is 25.4 µm. US film buyers normally say mil, though some also use gauge with the same 100 gauge to 1 mil relationship. Sheet-metal and wire gauge are different systems, where a bigger number means thinner material, and they do not convert with the formulas above. If a quote just says "gauge", confirm that it means film gauge.
Film thickness conversion table (8 to 200 µm)
| Micron (µm) | UK gauge | US mil | Reference point |
|---|---|---|---|
| 8 | 31 | 0.31 | Very thin film, under 15 µm |
| 10 | 39 | 0.39 | Very thin film, under 15 µm |
| 12 | 47 | 0.47 | Very thin film, under 15 µm |
| 15 | 59 | 0.59 | Equals the EU very lightweight limit, which applies below 15 µm |
| 20 | 79 | 0.79 | Thin film |
| 25 | 98 | 0.98 | Thin film |
| 30 | 118 | 1.18 | Light-duty film |
| 35 | 138 | 1.38 | Light-duty film |
| 40 | 157 | 1.57 | Medium-weight film |
| 50 | 197 | 1.97 | Equals the EU lightweight limit, which applies below 50 µm |
| 60 | 236 | 2.36 | Medium-weight film |
| 70 | 276 | 2.76 | Upper end of the England charge scope (70 µm or less) |
| 75 | 295 | 2.95 | Heavier film, above 70 µm |
| 80 | 315 | 3.15 | Heavier film |
| 90 | 354 | 3.54 | Heavier film |
| 100 | 394 | 3.94 | Heavy film |
| 125 | 492 | 4.92 | Heavy film |
| 150 | 591 | 5.91 | Very heavy film |
| 200 | 787 | 7.87 | Very heavy film |
Values are rounded: gauge to the nearest whole number, mil to two decimals. The reference column marks where the regulatory lines fall. Labels such as "thin" or "heavy" are rough descriptions, not trade grades.
Gauge to micron and mil to micron: common quoted values
| UK gauge | US mil | Micron (µm) |
|---|---|---|
| 100 | 1.00 | 25.4 |
| 150 | 1.50 | 38.1 |
| 200 | 2.00 | 50.8 |
| 250 | 2.50 | 63.5 |
| 300 | 3.00 | 76.2 |
| 400 | 4.00 | 101.6 |
| 500 | 5.00 | 127.0 |
| 600 | 6.00 | 152.4 |
| 800 | 8.00 | 203.2 |
| US mil | UK gauge | Micron (µm) |
|---|---|---|
| 0.5 | 50 | 12.7 |
| 0.75 | 75 | 19.1 |
| 1 | 100 | 25.4 |
| 1.5 | 150 | 38.1 |
| 2 | 200 | 50.8 |
| 2.5 | 250 | 63.5 |
| 3 | 300 | 76.2 |
| 4 | 400 | 101.6 |
| 5 | 500 | 127.0 |
| 6 | 600 | 152.4 |
Worked examples
Comparing three quotations. One supplier quotes 250 gauge, a second 2.5 mil and a third 60 µm. 250 × 0.254 = 63.5 µm, and 2.5 × 25.4 = 63.5 µm, so the first two are identical. The 60 µm film is 5.5 % thinner than 63.5 µm and equals 236 gauge, which can show up in the price per thousand.
Converting a specification. A drawing calls for 70 µm. 70 ÷ 0.254 = 275.6, so about 276 gauge, and 70 ÷ 25.4 = 2.76 mil.
From thickness to film mass. Film mass per square metre is thickness in µm multiplied by density in g/cm³. A 50 µm film with a density of 0.92 g/cm³ (typical for LDPE) weighs 50 × 0.92 = 46 g/m².
Where do the legal thresholds sit on the scale?
As of October 2026, three thresholds come up most often: two EU definitions and the England charge scope. They are factual pointers, not legal advice; what applies to you depends on your role and market.
- EU: Directive (EU) 2015/720 defines "lightweight" plastic carrier bags as below 50 µm (197 gauge, 1.97 mil) and "very lightweight" bags as below 15 µm (59 gauge, 0.59 mil). Regulation (EU) 2025/40 (PPWR) Annex V restricts very lightweight plastic carrier bags from 1 January 2030, with exceptions.
- England: the single-use carrier bag charge applies to plastic bags of 70 µm or less (276 gauge, 2.76 mil).
Blown film is never perfectly even, and specifications often allow a tolerance around the nominal figure, commonly in the order of ±10 %. A bag specified exactly on a threshold can therefore measure on either side of it. The detail is in plastic carrier bag regulations in the EU, UK and US.
What to write when you specify film thickness
- Give thickness in micron as the primary unit, with gauge or mil in brackets if your team uses them.
- Name the film (LDPE, LLDPE, HDPE or a blend), because 50 µm of one is not the same bag as 50 µm of another.
- State the tolerance and how thickness is measured, for example to a method such as ISO 4593.
- Put the thickness next to the bag or film dimensions and any print requirements in your request. The packaging RFQ guide lists the other fields a quotation needs.