The American “Metric” Ruler

By The Metric Maven

Bulldog Edition

Early in my metric-only odyssey I learned some metric lessons the “hard way.” Because of my  inexperience, I had a naïve view of metric implementation that caused me to be incautious. My better half decided she would try using metric for some of her craft work. She flipped her ruler over to its metric side and began using it. I thought nothing of leaving her alone to work, after all metric is simpler—right?  Within a few minutes she was complaining that the pattern she was working on was 1.5 mm long and she needed it to be larger.  I had seen the pattern and it was way larger than 1.5 mm. Incredulously I walked into her study, looked at the pattern, looked at the ruler and realized it was more like 15 mm in length. I inquired how on earth she measured 1.5 mm, she quickly showed me the marking on the ruler, and I realized that according to the ruler, she was indeed measuring 1.5 mm. Here is the end of that ruler.

Ruler which indicates mm graduations — But cm are numbered

One notes that it is labeled millimeters, and therefore one would expect, that like inches, each numbered mark, 1, 2, 3 and so on would be in millimeters!  I looked at it in astonishment, and realized that anyone not familiar with the metric system could easily make this mistake. I explained the situation that the large marks are centimeters and the small divisions
are millimeters. It was my first realization that American “Metric” Rulers (AMR) actually had two units, and the imperial side only used inches. Until I actually started using metric exclusively, I had never noticed this. One of my biggest complaints is the common mixing of units in imperial. For instance a person’s height might be 1 yard, 2 feet, 10 inches and 1 barleycorn tall. Ok, we have simplified this to just 5′ 10 1/3″ but that’s still two units–designated with quotation marks. The use of multiple units is a clear violation of Naughtin’s Laws and only serve to obfuscate the experience of a direct cognitive understanding of magnitude.

Centimeter label with cm designations

I realized that the  ruler should say cm instead of mm. This caused me to start looking at rulers offered in office supply stores. It is there, one can see that the metric side of a dual-scale ruler gets little respect. For instance, I went to an office supply store recently and purchased a green ruler, fabricated by a company which boasts they have made rulers since 1872. You can see that the designation is cm this time, but the origin of the scale is on the end which is rounded and used to hang the ruler on a wall. The inch side gets the square end which is psychologically more appealing. You don’t think this is a big deal? When you pick up a slice of pizza, how often do you begin eating the wide, crusted end?—rather than starting with the point? Simple ergonomics matter.

A ruler that acknowledges both cm and mm units are on it

But in reality, both millimeters and centimeters exist on this ruler. To my surprise, the store brand rulers have both mm and cm designated at the end. Someone actually thought about this and marked both! Unfortunately, it now gives one two possibilities for what the numerical marks might designate, instead of resolving the situation. Assuming one knows which are cm and mm,  a person can, for example, measure something with an American “Metric” Ruler, which is say 1.5 cm long. So how is this done? One first looks at the 1 cm designation, then counts the millimeters, and concatenates them with a decimal point to obtain the answer. You are always holding the first digit in your mind 1 and then counting to the next digit, which is 5 and then creating the answer of 1.5 cm. This is true even if you designate the millimeter graduations as tenths of centimeters. When I first received an Australian metric ruler, it had nothing but millimeters, and my mind quickly responded to its ease of use. The Australian who sent it to me said “I learned early on that centimeters cause mistakes, and in my business this cost me money, and I stopped using them.” He told me it took Australians a while to realize this, but more and more, he was seeing centimeters, less and less.

Custom metric rulers given to Metric Maven Clients

In my engineering work, I have never seen a metric drawing in centimeters. After I had used a metric ruler marked only in millimeters, I hoped I would never encounter one. A client who is an imperial die-hard informed me that there is no use using metric, you have to buy meat in pounds, and lengths in yards, or feet or inches in this country. I was told to “get real.” My reaction to his statement was not what I expected, my mind wandered back to my youth, when lumber yards, car dealers and others would hand out free yardsticks on the Fourth of July, Labor Day and on other important dates for advertising. I realized that I needed to hand out mm only rulers  to my clients, as I suspected many of my clients, despite all being engineering firms, had never seen such a thing as a mm ruler. I first tried to get wooden millimeter rulers from wooden yardstick suppliers. One of the vendors informed me, in no uncertain terms, that this is America and we use inches. Finally I came across a supplier who would make custom metal mm-only rulers for me. I decided to go with a 600 mm long ruler to hand out to my clients and their Engineers. I reasoned 600 mm would be long enough to measure most common designs found in my industry, which is microwave and antennas. The rulers are metric-only (no inches), have my company logo, name and information, just like the old wooden ones, which are now collected as antiques. The end of one of my mm-only metric rulers is shown in the inset above.

When I handed out the mm-only rulers, I was pleasantly surprised by the reactions. One Engineer said “Oh, thank heaven’s it’s 600 mm, that’s actually a useful length.”  Two others at another company took the opportunity to thank me for suggesting the centimeter be eschewed, they really found it simplified matters. One older Engineer said “It’s amazing, I’m starting to lose my feel for inches, and think in millimeters now. This ruler is great.” I was floored. I was used to a much more visceral and negative reaction, or one of dismissive semi-contempt. I later had lunch with two Engineers, one of which has seemed to enjoy his attempts at devil’s advocate for centimeters. He continued trying to needle me, and then quickly moved the ruler I’d given him closer to his person, and said “Now you aren’t thinking of taking this back—are you?” I replied “I can see that a ruler like this desperately needs to be with someone like you.” When I took a ruler to the Engineer who had told me to “get real,” his countenance was that of a person who had asked me to find a Unicorn, and I had obtained one, broke and saddled it for his riding pleasure, then delivered it to his door.

This is the first time, that I felt I might have made a small difference in American metrication, but why was this time different? My conclusion is the ubiquitous presence of American “Metric” Rulers. They offer very little obvious advantage, and probably are viewed as an equivalent to decimalized inches, or are seen as even more complicated with their mixture of cm and mm scales. I’ve come to believe more and more that American “Metric” Rulers are a big obstacle to Americans adopting metric for common everyday use. With millimeters, one almost never needs a decimal point for common measurements, but this simplicity is never experienced, or realized, because all that is around us are American “Metric” Rulers. A small step which might help metrication in this country, would be to mandate that ruler manufacturers change the “metric” side of our dual-scale rulers to millimeter only. It’s a minute change, but I think it might cause people to view the metric system more favorably, and even possibly use that side of the ruler more often. Dual scales (mm and inches) clearly violate Naughtin’s Laws, and conspire to put off metric use, but it would be some small victory toward mandatory metrication.

I have wondered many times since, that if, many years ago, I had attended local Fairs in the Midwest, where the metric side of the wooden yardsticks was in millimeters,  if we might not be much further down the path to metrication, and not continuing to stand still as we have been for over 150 years.

Related essays:

Stickin’ it to Yardsticks

The Design of Everyday Rulers

America’s Fractional Mind

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.

The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.

The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.

9 thoughts on “The American “Metric” Ruler

  1. It always seems to me that the manufacturers of both rulers and tape measures make their products difficult for the people that want to use metric measures. I have a high regard for the late Pat Naughtin and his saying “Dont duel with dual” This applies not only to metric/Imperial and metric/USC but also to cm/mm. There is however another unwanted feature of metric rulers and tapes. Have you noticed how it always seems to be difficult to read a metric ruler or tape compared to a USC or Imperial ruler or tape. Its because the mm markings on the ruler or tape have the same length. In your examples the 1,2,3,4,6,7,8,and 9 mm marking are the same length. Only the 5 mm is longer. Compare that to the USC/Imperial ruler or tape where the 1/2 inch marks length is different from the 1/4 inch, 3/4 inch marks length, and the length of the 1/8, 3/8, 5/8, 7/8, marks are different from both the 1/2 inch and 1/4 inch and 3/4 inch marks.
    I have seen a ruler where the mm marks have varied, the 1 mm was shortest and the 2 mm was longer, and the 3mm was longer again and the 4mm longer again and the 5 mm the longest. Rulers that have varied mm marks are easier to read but they are hard to find and are not widely available. I hope that ruler/tape manfacturers will see that making their products user freindly will lead to increased sales.

  2. One of the problems with moving to metric is finding quality and properly marked rulers. I would suggest you create a page that links to proper metric products.

    My first go at buying metric tape measures ended up with shipping from Austrailia and I ended up with a cm tape measure..

  3. Can you PLEASE post a website for that firm which makes these miraculous rulers?

    • I take it you are referring to the Maven’s unambiguously millimeter 600 mm stainless steel ruler. (You can’t see it in the picture, but it also has an extremely durable cork-like synthetic rubber backing, which makes it a really sweet for desktop work.)

      Unfortunately, there are difficulties. The scale was to the Maven’s own specifications, and there was a very short, one-off, production run. As you might expect, getting a ruler like this made in a short run was a fairly dear whim. And they were passed out in the course of engineering consulting. I wouldn’t be surprised if they’re all gone.

      The other problem is that the Metric Maven site is, and is intended to remain, completely non-commercial: no advertising, no selling. There have been metric advocacy sites that wound up chiefly selling cutesy/snarky tee-shirts, coffee mugs, and the like — if they didn’t start out that way. The Maven wants to remain unambiguously an advocate.

  4. Use of SI should include a familiarity with how it treats powers of ten, specifically, the fact that scale prefixes change only the scale, not the unit.

  5. One point the Maven missed in another excellent posting is that those store-brand rulers giving CM under MM (besides that these should be lowercase, of course) should have CM first with MM under it because of what he writes, namely it’s 1, 2, 3, … units, and those units are centimeters.

  6. Re Cm/mm ruler mixup:

    I live and was born in a “metric country”. Our rulers are almost always the way you don’t like, i.e. the numers refere to centimeters but the scale itself is in millimeters.

    I think the root of this is how schools teach length measurements to children. To make learning easier the first rulers children get only have a centimeter scale, without any millimeter marks. Easy to see and works even when you only can count to 10. When the children gets older they get rulers with millimeter markings but then the 0-30 scale is kept in some kind of effort to not confuse things. (The common lenght of 30cm probably has its roots in that its only a little bit longer than the long side of A4 papers (most common paper size in countries not using letter/legal paper sizes).

    I agree that rulers should be marked in millimeters, not centimeters.

    However I disagree that decimeters is a problem. It might be a problem when trying to introduce the metric system to someone used to the imperial system, but if you grow up in a metric country you have enough time to learn all prefixes.

    Centimeters is IMHO the most convenient measurement for for example furnishes, clothes, people, animals, blankets e.t.c.
    IIRC lenght in passports i metric countries are usually in centimetres.

  7. I buy metric rulers whenever I go to Europe. I still have quite a few left and quite a variety. I used to pass out the one metre rulers as awards at science fairs to students who used metric in their projects. I had to buy them from Austria because I could not find any metric only in the USA. I think Stanley makes a metal key chain metric only one meter ruler, but you have to buy 5,000 at a time. Anybody want to go in with me and get 5,000?

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