3 min read
One gauge is 0.254 microns. That is the whole conversion, and it is the same for refuse sacks, stretch film, shrink film and anything else made of polyethylene. 100 gauge is one mil, one thousandth of an inch, 25.4 µm.
The figure you have
Sacks only. HDPE carries more in tension per micron and much less against a corner.
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Gauge is one hundredth of a thousandth of an inch, so one gauge is exactly 0.254 µm. The sack trade rounds this to four gauge per micron — 200 gauge for 50 µm rather than the strict 196.9 — and both figures are shown so you can see which one a quotation is using.
Want this as a PDF? The answer above is yours either way. The PDF is the working written out — the figures you entered, the result, and the assumptions behind it — for a colleague or a purchase requisition.
The two readings you will see
The sack trade rounds the conversion to four gauge per micron, which is where the tidy numbers on a sack quotation come from — 120 gauge for 30 µm, 200 for 50, 500 for 125.
That rounding runs 1.6% light, and the gap widens with thickness:
| Gauge | Strict, × 0.254 | Sack trade, ÷ 4 | Mil |
|---|---|---|---|
| 80 | 20.3 µm | 20 µm | 0.80 |
| 100 | 25.4 µm | 25 µm | 1.00 |
| 120 | 30.5 µm | 30 µm | 1.20 |
| 200 | 50.8 µm | 50 µm | 2.00 |
| 300 | 76.2 µm | 75 µm | 3.00 |
| 500 | 127 µm | 125 µm | 5.00 |
Nobody argues about 1.6% on a sack, and neither do we. The one place it matters is a comparison: if you are putting two quotations side by side and one has been converted strictly while the other used the four-to-one rule, the cheaper one may simply be the one that was rounded more generously.
The thing that is actually different
You may have been told that sacks and stretch film use different gauge scales, and that the difference is large. They do not. We have seen the claim in trade material and it is wrong — the arithmetic above is the arithmetic for both.
What differs is what the number means, and that difference is enormous:
| Thickness | As a refuse sack | As a stretch film |
|---|---|---|
| 12 µm | light duty, office waste | thin machine film, high pre-stretch |
| 20 µm | light duty, swing bins | the common machine film |
| 30 µm | medium duty, general commercial | heavy machine film |
| 50 µm | heavy duty, garden and clinical | very thick, difficult loads only |
| 125 µm | rubble grade | not a stretch film at all |
Fifty microns is a routine specification for a garden waste sack and an extraordinary one for a stretch film. Convert the number correctly, apply it to the wrong product, and every figure downstream is right about a thing you are not buying. The converter shows both readings at once for exactly this reason.
The trap that actually costs money: HDPE against LDPE
This is the comparison that goes wrong in real quotations, and no unit conversion catches it.
HDPE carries roughly twice the tensile load of LDPE per micron. A 12 µm HDPE sack does the work of a 25 µm LDPE one. It is thin, it rustles, and for paper and dry packaging it is genuinely the right material rather than the cheap one — you use half the polyethylene for the same job.
LDPE stretches before it tears and takes a puncture that would open HDPE instantly. Anything with a corner, a bone, a broken bottle or a wet load needs it.
So a supplier quoting “20 µm” against your “40 µm LDPE” may be offering a like-for-like replacement in HDPE, or may be offering half the sack. The micron figure alone does not tell you which, and the specification sheet often does not say. Always ask for the polymer.
The converter reports the rough equivalence in both directions. Treat it as a tensile rule of thumb only: against puncture the ratio runs the other way, and no single factor describes it.
Mil, for North American specifications
One mil is one thousandth of an inch, 25.4 µm, 100 gauge. It turns up on specifications written for the American market and on machinery documentation.
The conversion is exact and the converter does it, but the caution is the same: a 2 mil sack and a 2 mil film are both 50.8 µm and they are not remotely the same product.
What we quote
Our quotations state thickness in microns, always, with the polymer named — LDPE, LLDPE, HDPE, and the recycled content if there is any. Gauge appears only where a customer asks for it, and then with the conversion shown.
If you are holding a quotation in gauge with no polymer stated, send it to us. Working out what has actually been offered takes about five minutes and it is free; it is also, more often than we would like, the moment somebody discovers they have been comparing two different products for a year.