What Is a Mil? Poly Bag & Plastic Film Thickness, Explained
Updated August 1, 2026.
A mil is one thousandth of an inch (0.001") — the standard unit for poly bag and plastic film thickness in the US. It is not a millimeter: 1 mil = 0.0254 mm, so a 2 mil bag is about 0.05 mm thick. Every poly bag, sheeting roll, and stretch film spec you'll see uses mil, and pick too thin and the bag tears at the seam in transit.
Mil conversion table
| Mil | Inches | Millimeters | Feels like | Typical uses |
|---|---|---|---|---|
| 1 mil | 0.001" | 0.025 mm | Produce-bag film | Lightweight liners, short-term dust covers |
| 1.5 mil | 0.0015" | 0.038 mm | Bread bag | Light parts, apparel, single-use packaging |
| 2 mil | 0.002" | 0.051 mm | Standard poly bag | The general-purpose workhorse: parts, documents, retail |
| 3 mil | 0.003" | 0.076 mm | Heavy freezer bag | Hardware, moderately sharp parts, food storage |
| 4 mil | 0.004" | 0.102 mm | Thick, semi-rigid | Industrial parts, metal components, bulk storage |
| 6 mil | 0.006" | 0.152 mm | Tarp-like | Sharp or heavy parts, construction, long-term storage |
| 8–10 mil | 0.008–0.010" | 0.20–0.25 mm | Rigid sheet | Extreme-duty containment, abrasive contents |
How to choose a mil thickness
Match the thickness to the failure mode you're preventing. Tearing on sharp edges calls for 4–6 mil; simple dust and moisture protection needs only 1–2 mil; anything shipped loose inside a carton usually lands at 2–3 mil. Doubling the mil roughly doubles the material in the wall — and the cost — so buying heavier than the job wastes money at case quantities. When two thicknesses both work, the per-bag price at your case count settles it.
Frequently asked questions
Is a mil the same as a millimeter?
No. A mil is one thousandth of an inch (0.001"); a millimeter is roughly 39 mils. Mixing them up is an expensive mistake — a "2 mm" bag would be nearly 80 mil, tarp-thick.
What mil poly bag do I need for shipping?
For most products shipped inside a carton, 2 mil protects against dust, moisture and scuffing. Step up to 4 mil for hardware and edged parts, and 6 mil for heavy or abrasive contents that would work through a lighter wall in transit.
How do I measure the mil of a bag I already have?
Use a micrometer on a single wall (not a folded edge) and read thousandths of an inch. Reputable suppliers publish the nominal mil on the product page — every Packrift poly listing carries it in the title.
See the full poly bags range or the 2 mil vs 4 mil comparison for a deeper side-by-side. Sizing questions? Ask us.