Why are capacitor sizes rarely expressed in nanofarads?

Question

Many capacitance values occurring in electronic circuits can be conveniently expressed in nanofarads, e.g. "a 10nF decoupling capacitor" .

However, the use of the term "nanofarads" or its abbreviation "nF" is often avoided and instead the numerically equivalent terms "10000pF" or "0.01μF" are used. The first term is three characters respectively two syllables longer while the latter is two characters respectively five syllables longer. This seems inconvenient, so there should be a reason for that.

Nanofarads are avoided by

• distributors, e.g. Digikey, Mouser, Farnell, but not by RS;
• manufacturers, e.g. AVX, Kemet, Wima, but not by Vishay;
• and engineers, e.g. Robert Kollman from Texas instruments.

As an example reference, here is a screenshot from Digikey:

Interestingly, resistances and inductances are generally stated without avoiding a particular prefix.

Answer 1

They don't. I'm American and I use nano for Farads like any other prefix, which is when doing so would put 1-3 digits to the left of the point.

A long time ago, nF wasn't used much for whatever reason. This wasn't a American thing as much as a long time ago thing. I've even seen pF referred to as µµF. Even worse, that was sometimes abbreviated to "mF". Over time these ancient designations have been depricated, and now we routinely use mF, µF, nF, and pF.

Other places where high technology meant a metal plow behind your horse while we were using vacuum tubes didn't pass thru this phase. When they got around to learning to spell "EE", the common metric prefixes for powers of 1000 were already in common use. One disadvantage of being early leaders is that you can end up with some baggage when common conventions eventually emerge.

I have mentioned this exact issue to some distributors when seeing a dropdown list like you show. They say that there are still a few obstinate old farts out there that get upset or confused when you show them nF and mF, so they avoid those. Time will fix this, and largely already has.

Answer 2

I think its just because it is a middle ground and so using just uF and pF, we can usually classify where a capacitor is being used just by that unit and then partially the value. If we were to use the nF more predominantly, it may become more difficult to discern where that is being used.

Just spit-ballin.