Does metric-only labelling require changes to package sizes?

An argument made against metric-only labelling in the US is that manufacturers would need to change packaging to rational metric sizes. Ronnie Cohen looks at the UK’s experience over the past 50 years.

The need to change package sizes is sometimes seen as an obstacle to the adoption of metric-only labelling in the US, and may also be a reason for the continued use of supplementary indications in the UK and, to a lesser extent, in the EU. We will therefore examine the myth that:

“Metric-only labelling requires changes to package sizes.”

When there is a transition from imperial to metric in manufacturing, there are two ways to manage the change, namely hard metric conversion and soft metric conversion (and no, this has nothing to do with Brexit).

Hard metric conversion

In the context of metrication, a hard conversion occurs when an imperial-based package size is rounded off to a close rational metric size. For example, packs and tubs of butter used to be sold in half pound (227 g) and one pound (454 g) sizes. Now, they are usually sold in 250 g and 500 g packs. This is an example of hard conversions where the packages were changed to rational metric sizes.

Here are a couple of examples of products sold in rational metric sizes:

Soft metric conversion

Products labelled exclusively in metric do not need to be sold in rational metric sizes in the UK. There are many examples of  products that underwent soft metric conversion. For example, jam is still still sold in the same sizes as before the metric changeover. The only thing that has changed is the weight shown on the label; they now show 454 g instead of 1 lb and the 12 oz jar lives on as 340 g. However, other suppliers have switched to the metric rational sizes of 450 g and 500 g.

Here are a couple of examples of products sold in non-rational metric sizes:

Jelly_454g Jam_454g

Bottled beer is occasionally sold in pint-sized bottles but labelled exclusively in metric units. While there is some beer and cider on sale in the UK in pint-sized bottles and/or cans, beer and cider sold in supermarkets and off-licences are mostly sold in rational metric sizes. And, of course the supermarkets sell fresh milk in rational imperial sizes, 1/2, 1, 2, 4 and 6 pints, whereas the corner shop and the garage will probably stock rational metric sizes, 500 mL, 1 L and 2 L.


The notion that metric-only labelling will require round metric package sizes is unfounded. When the US Fair Packaging and Labeling Act eventually allows metric-only labelling, manufacturers are likely to have a choice between hard conversion and soft conversion.

6 thoughts on “Does metric-only labelling require changes to package sizes?”

  1. Metric only labelling may not automatically mean a move to rounded metric sizes, but silly metric sizes leaves a bad taste in consumers mouths. During the 1970s, the media in he US waged a war against metrication and was successful simply by scaring the public with horror stories of odd numbers that metrication will bring.

    Nothing will change we were told, just the numbers on the packages. You will still buy a pound, but now it will be 0.45359237 kg. Everyone will have to order food in increments and decrements of this strange value. We will still have miles, but they will be in increments of 1.609 344 km. Inches will be in increments and decrements of 2.54 cm. Even to this day on packaging, decimalised centimetres are encountered with plenty of decimal dust in comparison to a nice round inch value. Probably to subconsciously remind consumers of what numbers you will see if the USC is dropped and metric only is present.

    The media scare campaign worked in that the population rose up against metrication.

    The people behind the FPLA, the FMI (Food Marketing Institute) know very well that metric only labeling in the US with metric only and silly numbers will bring and uproar as well as a drop in sales.

    The situation in the UK was different. Metric sizes were slightly smaller in many cases to their imperial equivalent. So, producers so no issue in going from a pint of 570 mL to a 500 mL package with out a reduction in cost. In the US, just the opposite would occur. A 470 mL pint would have to be up-sized to 500 mL and in order to keep the peace the prize can not rise. Thus the producers would be losing profits.

    The present FPLA does not dictate sizes and producers are free to choose rounded metric if they wish and some do, such as soda pop and other drinks. This also includes imported products. The FMI is most likely not happy with this situation where a 2 L soft drink only requires 2 characters on a label, whereas the USC equivalent with a combination of floozy ozzes and quarts takes up a whole one side of the bottle label. Some 2 L bottles however now only list 2 L (2.1 QT). But, since only a small percentage of products fall into this category it hasn’t caused a trend.

    Even if the FPLA were to be amended it is doubtful many products will drop USC unless they are already in rounded metric sizes and the USC just adds clutter to the label. Foreign products that occasionally do so may see fit to drop the USC, but that may work against them if the consumer becomes turned off to the product. Since producers are required to provide a US standard nutrition label for products sold in the US, there will still have to be a different label for US bound products anyway. The only way to avoid this is to come up with a universal nutrition label.

    In light of the adamant attitude of the FMI to having the FPLA amended to allow metric only, the EU should reciprocate by forbidding USC or imperial on labels or products destined for the EU market. At least this way what is sauce for the goose is sauce for the gander.


  2. I’m just curious about UK and EU labels. What percentage of packages encountered on the supermarket shelves are actually dual labelled? Even a rough estimate would work.


  3. Nothing is “written in stone” until Congress amends the law, and NIST has not yet formally introduced the proposal to Congress. The proposal dates to at least as early as 2002, and has been sitting in its current, unpresented-to-Congress form since 2009. I largely despair of it ever being put to a vote; further, at the moment, Congress couldn’t agree the sun will rise tomorrow.

    However, in an attempt to quell this misconception, NIST has added the final phrase to their proposed version of the amendment relative to package size in Section 1462:
    “Nothing in this chapter shall be construed to apply to unit pricing, advertising, recipes, nutrition labeling, other general pricing information, or to require changes in package sizes.”

    However, since metric-only would be optional, I believe it is quite likely that those manufacturers who already have rational metric sizes would be the first to drop Customary and that would create some informal pressure to develop a rational metric size at the same time as going metric only. (But, it would NOT be a matter of law.)

    Compared to the UK, the US has virtually no “standard size” legislation (wine and spirits are an exception) and new sizes are pretty frequent. There is an escape clause. If the Secretary of Commerce feels there is an excessive proliferation of sizes in a particular commodity, he can appeal to the responsible trade organization to bring some order to the situation. If this is ever used, it is used behind the scenes, and certainly isn’t common. Manufacturers seem to agree through trade organizations on a number of quasi-standard sizes acceptable to the US public, although the number of sizes does seem to surprise some visitors here. Unit pricing is largely voluntary in the US, but very widely adopted so size proliferation doesn’t make value comparison too difficult.


  4. I’ve already seen more packages here in the USA that are rational metric sizes than I would have expected.

    As Ronnie says, once the FPLA is amended to permit metric-only labeling, those packages will lose the “Imperial” units (often in first place) and leave just the rational metric units (without the surrounding parentheses any more).

    And as Ronnie says further, other packages will either get changed to rational metric or go through soft conversion. Either way, I believe metric-only packages will quickly dominate.

    That will certainly heighten awareness of metric and help set the stage for conversion here in the USA.


  5. I continue to see more product packages in the USA displaying a more-or-less rational metric quantity along with the equivalent quantity in US Customary (rather than a rational USC quantity followed by some weird-ish and totally unmemorable metric quantity).

    Latest sighting on my part for this sort of thing is a chain grocery store’s house brand selling organic raw honey as NET WT 680g (1 LB 8 OZ).

    And, yes, the metric is printed first followed by the USC in parentheses. While this is less common than USC first and metric in parentheses (albeit with the more “rational” quantity being metric), I am seeing more and more labels with the metric listed first with a reasonably rational quantity.

    If we ever get around to amending the FPLA (Fair Packaging and Labeling Act) over here to permit metric only labeling, I am confident there will be an ever growing movement in the USA to label products in metric only. That could be the opening round of a real commitment to finally convert the USA to metric.

    2020 elections, anyone? 😉


  6. @Ezra Steinberg:

    Whether the jar has a fluid capacity (middle of the neck?) of 500 ml or 1 USA customary [short] pint will be the dead giveaway. Sometimes a 10 g increment is just a 10 g increment, to paraphrase Sigmund Freud…

    FWIW, a large proportion of the factory-farmed honey in UK shops seems to be 340 g (half of 680 g), 454 g or 227 g ☹.


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