Soft (In The Head) Metric

By The Metric Maven

Not long ago I was in an engineering meeting, and the persons involved were using inches. I attempted to convince them to use metric instead. The design was then quoted using a strangely odd number. With millimeters, the dimensions should now be round integers for the mounting plate and other design options. I protested that the design did not appear metric even though the dimensions were dual. The engineer looked back at me and said, yes it’s metric, we use soft metric here. I’m sure my jaw became slack when I realized what he was saying. I replied “soft metric is no metric at all.” After considerable discussion, I realized that I was yet again going to lose when it came to using actual metric in a US engineering environment.

One of the first times I encountered the idea of soft metric was in the monograph Metric Implementation in U.S. Construction by Andrew J. Holland. This report was written for Holland’s Master’s Degree in 1997. Here is how it defines hard and soft metric:

Optimistically Holland states that only a few products will need to be resized for hard metric:

A handful of products which are considered to be modular products, such as suspended ceiling grids, drywall, plywood and rigid insulation, raised access flooring, brick, and concrete block fall in the category of “hard-metric” and therefore will need their dimensions changed to the new rounded metric numbers.

…and that 95% of products will not need to be altered. While this sounds promising, those affected in the US will ask for “exemptions”  which will become permanent, and then nothing will change. Take NASA for example, the rocket scientists there have been issued metric exemptions for decades. Any drawings they would ever generate in a “metric switch-over” would probably have both metric and Ye Olde English,  would continue to be drawn in Olde English inches, and after a time no one would see why metric is a superior idea, and go back to inches, like the California DOT did. Here is the US escape clause for construction:


The idea is to change all of the important (modular) stuff to metric so the numbers will all be simple ones:


Unfortunately, we must be “flexible,” so there are exemptions for sheet metal thicknesses and such:


The term gauge is meaningless and a fountain of confusion. Gauge values need to be given priority for reform. I have written about this problem in my essay Don’t Get Engaged With Gauge.

This type of metric change might possibly work in the building construction industry, if a mandatory metric-only metrication (no dual units) was implemented and most soft metric eschewed. In practice it has been crushed by the building industry. The idea of soft metric has been exported to other engineering disciplines in the US by those who want to maintain the status quo. That is what I’ve experienced in industry. Soft metric was waved in front of me as a distraction so Ye Olde English could continue to be used as soon as I left the room—and so that no metric changes would despoil our perfect engineering life in the US. The drawings might continue to have metric dimensions on them side-by-side with Ye Olde English, but the metric values would be ignored for the familiarity of the inch versions as Naughtin’s first law predicts.

Soft metric is pretend metric.

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The Metric Maven has published a new book titled The Dimensions of The Cosmos. It examines the basic quantities of the world from yocto to Yotta with a mixture of scientific anecdotes and may be purchased here.