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Jeff, he of the mightyOhm, asks:

Have you ever wondered why standard 5% resistors have strange values, like 330 and 470 Ohms, instead of nice round numbers like 300 or 500 Ohms?

It turns out that standard resistor values form a preferred number series defined by the EIA.  5% values are part of a standard called E24.  The standard is based on a geometric series – each value is approximately 1.1 times the previous one in the set.


EIA Resistor Values Explained
[via The Steampunk Workshop]

Gareth Branwyn

Gareth Branwyn

Gareth Branwyn is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor for Boing Boing and WINK Books. And he has a new best-of writing collection and “lazy man’s memoir,” called Borg Like Me.


2 Responses to EIA resistor values explained

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  1. KNfLrPn on said:

    I remember when I figured this out. I was so proud of myself. And if you look at 1% resistors, it’s the same thing but at a finer resolution.

    If you think about it, there’s no reason to have a higher resolution than the accuracy of the resistor.

  2. Metalworking on said:

    Like linear dimensions with the “Renard numbers” : R5, R10, R20, and R40 … or the rounded values…

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