I’m learning lots of new things as a result of this project and a concept I became aware of early on was “rational sizing.” I’m writing about this subject now because there’s been a lot of traffic on this idea on the U.S. Metric Association’s listserve under the name “oddball measurement.”
What it basically means is that when moving from U.S. customary units to metric ones, things might not end up with what some people call “rational” (or rounded) numbers. I was also told by a reliable source (thought I have to admit that I have not yet confirmed this) that rational sizing was one of the points of resistance by the food industry back during our last metric push in the mid 1970s.
I’ll try to explain:
If you have a traditional U.S. eight-ounce container and you want to move to the metric system, you have two options 1) retain the same packaging and “re-label” (though metric units are on most American packaging) the container as 236.588 milliliters (not sure how precise labels need to be), or 2) you resize the package to something that seems more “rational” like up to 250 mL or down to something like 230 mL. Apparently, in some people’s minds numbers that end in zeros or represent commonly used numerical breakdowns such as 25, 75 are more “rational.” I don’t personally have that bias but different minds work in different ways. (I supposed a third option would be to keep the packaging size the same and round down the milliliters it contains to a rounded amount but that doesn’t seem to be the direction most companies take.)
For example: within my reach (I’ve confessed to my laziness before) is a bottle of Elmer’s Craft Glue. Its label states that it holds “4 FL OZ (118 mL).”
My understanding (and I’ll confess to being overly dramatic here) is that 30 years ago the food industry in this country had two objections to going metric and one related to rational sizing. “Oh my God,” said the food industry, “if we go metric we’re going to have to move to rational sizing, which means we’ll have to change all of our packaging, and that will be expensive, and then nothing will fit correctly on the shelves in the stores, and we’ll have to change the size of the shelves as well. That’s an impossible thing to ask us to do.”
I consider this argument poppycock and not the popcorn kind.
When the time comes (though I don’t expect to have any actual say in the matter), just take the customary units off and let the metric units stand on their own until a redesign dictates new packaging and then make a minor adjustment in the volume if having a “rational number” is all that important (and I’m not convinced it is). Heck, I could see manufacturers use their traditional “sleight of hand” and make the packaging slightly smaller and keep the prices right where they are. This has historically been done many, many times and Consumers Reports magazine highlights these sorts of tricks on a regular basis.
Actually, after a quick look around, I now have in front of me a bottle of Sutter Home Champagne Vinegar and its label reads “12.7 FL. OZ. (375ml).” In this case, it’s the milliliters that are “rational” and yet I bought it even before I started my metric quest. I’m sure at the time, having a less rounded number for ounces didn’t phase me in the slightest.
So, if you hear the “rational sizing” argument thrown around in future in a move to the metric system, at least you’ll have some background on what it’s all about.
As far as I’m concerned, rational sizing is not a rational argument.
Linda
Note: The phrase “rational number” in the above context does not represent its true arithmetic meaning. For more information on that use see http://www.britannica.com/EBchecked/topic/492011/rational-number. Be prepared that most definitions I found required an understanding of the words “integer” and “quotient.”
More Than A Mile Behind: America and the Metric System 
One thing that rational sizing helps with is price comparisons. Here in Australia rational sizes wee introduced for a lot of goods on supermarket shelves when we went metric, which made it easy to compare value for money for the same can of beans from different manufacturers.
A few years ago these restrictions were eased, so tins and packets now have all sorts of numbers of grams or millilitres on them. (I have seen a few products in 455gram packages – one pound!) One thing that has helped in this regard is that supermarket shelf labels now have to have price-per-measure labeling, although this can switch between $ per kilogram and $ per 100g, even in the same store.
I have a package of Caramel Tim Tams in front of me, made by Arnott’s in Australia sold with a Pepperidge Farm wrapper here in the USA. It is 6.2oz (176g). It holds 9 biscuits.
Obviously rational sizing is BS
Not only that, with brands being multinational now, wouldn’t it make it much easier for them to consolidate package sizes?
You’re right about ‘rational’ sizes is poppycock, the food industry is constantly changing content and container sizes, and all of it down sizing but cost the same or upped the charge. One exception, soda pop.
I think if you conducted a full inventory of your consumer goods, you would find that the vast majority are “rational” in metric units not customary units already. It’s an easy argument to make, some countries where the govt promoted (forced) metrication have laws about sizing. As far as I know, the US does not- just labeling. Therefore, if you want to sell your product globally, then the rational thing to do is make it acceptable everywhere. For example, my Listerine bottle is 250ml, my bottled water is 1.5 liters, soda is in a 2 liter, etc. These metric sizes do not stop US citizens from buying these products. We really must move from thinking about consumption as gas, milk, and meat, these are such as small percentage of the total items we consume.