Film thickness is the single biggest factor in how strong a poly bag is and how much it costs. The same thickness is written in different units depending on who you ask: micron is the most widely used, gauge is still common in some markets, and mil is standard in the United States. Use the calculator above, or the table below, to compare them.
Micron to gauge and mil conversion table
| Micron (µm) | Gauge | Mil | mm |
|---|---|---|---|
| 10 | 39 | 0.39 | 0.010 |
| 15 | 59 | 0.59 | 0.015 |
| 20 | 79 | 0.79 | 0.020 |
| 25 | 98 | 0.98 | 0.025 |
| 30 | 118 | 1.18 | 0.030 |
| 40 | 157 | 1.57 | 0.040 |
| 50 | 197 | 1.97 | 0.050 |
| 60 | 236 | 2.36 | 0.060 |
| 75 | 295 | 2.95 | 0.075 |
| 100 | 394 | 3.94 | 0.100 |
| 150 | 591 | 5.91 | 0.150 |
| 200 | 787 | 7.87 | 0.200 |
How the bag weight is calculated
A bag is made from two layers of film, front and back. The weight of plastic in it is the film area multiplied by its thickness and the density of the material:
Weight (g) = 2 × (width + gusset) × length × thickness × density
- Width, length and gusset in centimeters (1 inch = 2.54 cm)
- Thickness in centimeters (1 micron = 0.0001 cm)
- Density in g/cm³: about 0.92 for LDPE and LLDPE, and 0.95 for HDPE
Worked example
A flat 12 × 18 inch LDPE bag at 50 micron: 2 × 30.48 cm × 45.72 cm × 0.005 cm × 0.92 g/cm³ ≈ 12.8 g per bag, or about 78 bags per kilogram.
Choosing a thickness
There is no single right thickness: it depends on what goes in the bag, how heavy and sharp it is, and how the bag is handled. A stronger material can also do the same job at a lower thickness. For example, an LLDPE-rich blend often outperforms a thicker plain LDPE film on puncture resistance. Our LDPE vs HDPE vs LLDPE guide explains the trade-offs.
If you're unsure, tell us what you're packing and its weight when you request a quote, and we'll recommend a thickness.
