Opening Up a Can of Morass

By The Metric Maven

Bulldog Edition

My father once worked in a corn canning factory, and has many tales from his tenure there. The one story which always comes to mind is that of a co-worker, called Roscoe, who marched to a different, and rather stochastic drummer. Roscoe never seemed to be able to get his time card to remotely match his apparent work schedule. One day his boss blew his top after seeing Roscoe’s time card and demanded he immediately come into his office. The boss looked at Rosco and inquired about the entries on his time card.


Boss:  I’ve looked at your card for this week and on Wednesday it indicates you worked 25 hours on that day.

Roscoe:  Yeah.

Boss: Roscoe, could you please explain to me how you could possibly have worked 25 hours on Wednesday.

Rosco: I didn’t take lunch that day.

It was tales like that which made me believe that the canning plant was operated by a mad hatter, with help from Bizzaroworld.

Recently my father sent me this table from a new cookbook:

How could I help but wonder if Roscoe had been tasked with determining the can nomenclature and quantity. An eight ounce can is 1 cup, which makes as much sense as any of the Ye Olde English Arbitrary Grouping of Weights and Measures do. Who would have thought that the next size up from an eight ounce can would be a picnic sized can? Every Midwestern picnic I’ve ever attended would always have cans of Van Camp’s Pork and Beans, “freshly opened” for the occasion, right in front of my eyes. Their website indicates the available cans are in 8 oz, 15 oz, 31 oz, 53 oz, and 114 oz sizes. Well, the cookbook has the wrong table so we’ll re-write it to conform with the VCPB default units:

Contents of Standard Cans:

8 oz Can = 8 ounces
Picnic = 10 ounces
No. 300 = 14 ounces
No. 1 tall = 16 ounces
No. 303 = 16 ounces
No. 2 = 20 ounces
No. 2 1/2 = 28 ounces
No. 3 = 32 ounces
No. 5 = 58 ounces
No. 10 = 80 ounces

The cookbook only matches one value of  VC Pork and Beans. They do not have a “picnic” size can. How on earth was I able to go on all those picnics? Was it a massive cover-up by the well-meaning women of my childhood? My father indicated that the corn canning plant at which he worked, exclusively used No. 303 cans. But how would he know if someone slipped some contraband No. 1 tall cans into the to loading dock?

Among my eclectic collection of books about engineering and science, I have zero references on standard sized “tin cans.” Wikipedia, as usual does not disappoint, and has a section on standard sizes. I’m sure the diligent volunteers there can clear up the confusion:

Can sizes in the United States have an assortment of designations and sizes. For example, size 7/8 contains one serving of half a cup with an estimated weight of 4 ounces; size 1 “picnic” has two or three servings totalling one and a quarter cups with an estimated weight of 10½ ounces; size 303 has four servings totalling 2 cups weighing 15½ ounces; and size 10 cans, most widely used by food services selling to cafeterias and restaurants, have twenty-five servings totalling 13 cups with an estimated weight of 103½ ounces (size of a roughly 3 pound coffee can). These are all “U.S. customary” cups, and not equivalent to the former Imperial standard of the British Empire or the later Commonwealth.

Wait a minute? The picnic size has 1 1/4 cups, which the last time I checked my Ye Olde English references was volume, which would translate into 10 fluid ounces, but it is designated as about 10 1/2 weight ounces? My understanding is that one fluid ounce of water = 1.0425 avoirdupois ounces more or less, so 10 fluid ounces of water is approximately 10.425 weight ounces. This is the picnic size which has an estimated weight of 10.5 ounces. This assumes the density of beans is the same as the density of water.

Apparently this means I should have written the table:

8 oz Can = 8 fluid ounces = 8.34 ounces
Picnic = 10 fluid  ounces = 10.43 ounces
No. 300 = 14 fluid ounces = 14.59 ounces
No. 1 tall = 16 fluid ounces = 16.68 ounces
No. 303 = 16 fluid ounces = 16.68 ounces
No. 2 = 20 fluid ounces = 20.85 ounces
No. 2 1/2 = 28 fluid ounces = 29.19 ounces
No. 3 = 32 fluid ounces = 33.36 ounces
No. 5 = 58 fluid ounces = 60.46 ounces
No. 10 = 80 fluid ounces = 84.4 ounces

When Van Camp’s gives their can sizes in ounces, is it fluid ounces or weight ounces?—with avoirdupois assumed? Perhaps Wikipedia can shed more light into this morass:

In the United States, cook books will sometimes reference cans by size. These sizes are currently published by the Can Manufacturers Institute and may be expressed in three-digit numbers, as measured in whole and sixteenths of an inch for the container’s nominal outside dimensions: a 307 x 512 would thus measure 3 and 7/16″ in diameter by 5 and 3/4″ (12/16″) in height. Notice that this is not in millimetres. Older can numbers are often expressed as single digits, their contents being calculated for room-temperature water as approximately eleven ounces (#1 “picnic” can), twenty ounces (#2), thirty-two ounces (#3) fifty-eight ounces (#5) and one-hundred-ten ounces (#10 “coffee” can).[9]

Ok, so “new” cans are all given as a volume of the outside of the can in 1/16 inch increments, but the “old” can numbers relate to the weight of room-temperature water? As the rest of the world might actually think we in the US did something rational with a measurement, they have to warn them that the can numbers do not relate to millimeters.

The Can Manufacturers Institute has this to say:

The CMI Voluntary Can and End Dimension Reference Manual is a compilation of technical information developed by committees of the Can Manufacturers Institute (CMI). Intended for use by CMI members and other interested industry representatives, this publication is available to the public as a service of the Can Manufacturers Institute. CMI does not provide either an expressed or implied warranty as to their viability or accuracy. – See more at:

Ah, yes, following long established US tradition, the values provided by industry are all voluntary and they are not to be held responsible if the values are not used or met or whatever. How dare you think they might be held to measurement standards. Here are the very, very, voluntary values:

So what values are used in metric countries? According to Wikipedia:

In countries and regions that use the metric system of measures, most tins are made in 250, 500, 750 ml (millilitre) and 1 L (litre) sizes (250 ml is approximately 1 cup or 8 ounces). In situations where products from the USA have been repackaged for sale in such countries, it is common to have odd sizes such as 3.8 L (1 USA gallon), 1.9 L (1/2 USA gallon), and 946 ml (USA 2 pints / 1 quart).

In metric countries one would expect volume in milliliters and/or mass in grams. Both would be very good.  My pantry shelf indicates that cans of beans and sauces in the US are all given in weight, so the only two values on the label are in weight in ounces and mass in grams. Therefore one much ask a simple question: “why did the cookbook offer the contents in cups?–which are clearly volume—when they are sold by mass?” The simple answer is I don’t know, and I doubt they would have a rational answer either. The designation of cans in the US is archaic, irrational and yet again shows that leaving the magic of technical Darwinism to determine the labeling of quantities in our economy only produces a chaotic situation which only confuses and does not offer clarity. Because this is the case, we are only left peering into an an open can of worms because we have never had a mandatory metric system switchover in the US.

7 thoughts on “Opening Up a Can of Morass

  1. Metrication dialogue usually includes the notion that, when the changeover comes to America, the several sectors of U.S. society will have a product-standard moment, and tackle the discord discussed in this article. One presumes this would mean a reduction in the number of different sizes. But, careful! To mention standardization of product sizes in America via metrication is to exhale anathema! Manufacturers bristle at the idea that someone is going to tell them which sizes they can, or even should, make. Here is where my “rational” adjective for U.S. metrication comes in. By no means go telling the makers WHICH sizes to make. They will start with metric units, but leave the opportunity for streamlining in THEIR hands. Set the standard and the plan, Congress, but leave the details of the conversion within each sector. Mind you, I say the MEASUREMENT standard SHALL be metric, but the PRODUCT design MUST be left in the hands of market forces. Do you hear me, FMI? Relax, FMI.

  2. The answer is pretty simple. Cans hold volumes because they have dimensions. Standard-sized cans will have standard (but perhaps quite arbitrary) volumes. A given size of can will always hold the same volume, but the mass of what it will hold depends on density.

    By law the contents of the can if solid, or solids in liquid, or a viscous or paste-like liquid must be labelled and sold by mass. So depending on density, a given volume can will hold a range of masses, depending on product. To further complicate matters, some cans are sold by drained weight if the liquid is not commonly consumed, but are sold by total weight if the liquid is used in food preparation (canned tomatoes are good example of sales by total weight).

    A recent copy of Metric Today had an article about selling honey in Canada (in metric). Honey can only be sold by mass in certain standard sizes and none of the standard glass bottles would hold the mass because of the density of honey. Not to defend the crazy Customary sizes, but similar problems can occur in metric countries. Of course Customary ounces can be either mass or volume which perhaps adds to the confusion.

  3. There is an element to all this unmentioned. Remembering a calculus class from long ago – the ratio of the diameter to height of a can is optimized in order to minimize material – yes this matters. (see but why tuna cans?)

    Then next issue becomes the case size being compatible with low cost shipping – which is depends on the can size. Case sizes also want to be optimized for cost of the box – ability to pack in shipping containers etc..

    Once again – we have the positive-feedback of established practices influencing the path to metrication. I think all of this will be solved right after garden hose connectors are improved and replaced.

  4. Why do we continue leaving to bad market forces the changeover to metric units? Was there any “confrontation” in industries of the nations since they changed to the Universal System Measurements (USM) better known as the impractical name SI, or Metric System? Why do we continue on this devastation of mistakes speaking of leaving to the market forces something that MUST be adopted from to the changing world already in the middle of the 2nd decade of the 21st Century for better venues in trade and commerce inside our country?
    I see now why many saying we need to change to the new metric units format are criticizing others with the same efforts. I was insulted by one of the USMA representative years ago who alleged that I wanted to throw “MOLOTOV COCKTAILS” just because I was trying to get their attention in which I said they can do more as representatives of an organization with many Metric Officers for almost all regions in the US and to pursue a real change to the Universal System of Measurements (USM) or SI.
    Mr. The Metric Maven, I am asking again for articles directed to members of our Public Educational System from elementary to higher education, that is to say, basically to Administrators of Public Educational Institutions. The majority of actual Presidents and Vice Presidents in Public Colleges and Public Universities do not like to touch this educational topic. Many of them are skeptics and refuse to give the necessary importance to this hated system of measurement by many in the U.S.
    On April 2011, I sent a manuscript on the Metric System to the “COMMUNITY COLLEGE JOURNAL” for possible publication and its main editor at that time, Mrs. Norma Kent, rejected it because of “…FOR OUR PRIMARY AUDIENCE (COLLEGE PRESIDENT AND SENIOR ADMINISTRATORS), THE METRIC TOPIC IS NOT ONE WE WILL LIKELY COVER.”
    This blog published a very good article for the NIST and I agreed with it. I again encourage you to write on this blog articles where the main theme were guided to our Public Educational System. Maybe, this is not your major concentration of interest at this point, however, I think articles toward those people (millions) working for educational institutions are very important at this time.

  5. In today’s [Monday’s] NYTimes columnist Charles M. Blow had his essay on minorities in STEM, which I would have liked to have posted a comment on but didn’t get to reading it until the Comments were closed.

    Anyway, I read many of the posted comments, but clicked on “Recommend” for only one, which I thought those in this forum would also like to read. Thus, it is pasted here:

    Bouddica earth 16 hours ago
    Children are easily influenced. When I was in 2nd grade I was learning measurements (US Customary Units) I was working on the homework problem of measuring our yard with in the front of the house in yards. I had a 12″ ruler and chalk so it was easy enough but then I couldn’t remember how many feet were in a yard so I asked my mom. She told me a yard is as long as our yard so it was as long as it was. Of course I got the answer wrong on my homework. When I complained to my mother she told me it wasn’t her fault – math is for men and only men understand. Girls, apparently, could only learn to add and subtract.

    I spent, just like all children in the USA, learning the US Customary Unit of mathematics. What a waste of time. The US Customary Unit and the Imperial Unit make math extremely complicated. In the hospital we used metrics. I quickly saw the advantage of metrics over fractions. If the US wants to compete then they need to switch to metrics and stop telling and demostrating to children how difficult math is by insisting on using an arcane systems that was never intended nor workable in today’s technology driven age.

    I’m married to a scientist/engineer, I’ll tell you what Europe, China, and probably the rest of the world think about American’s failure to succeed with the STEM. The opinion is that America prefers to import doctorates in STEM rather than spend the money on the education that would produce the experts.

    189 Recommended

    • About women and math:
      Two words: Rachel Riley.
      Two more words: Danica McKellar.

    • Also, as for “traditional” women and knowing how long a yard is:

      Women used to make their own clothes.
      Cloth is (at least in the U.S.) sold by the yard.
      So yes, women would have been very familiar with the yard as a unit of measure.

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