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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 is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of a dozen books on technology, DIY, and geek culture, including the first book about the web (Mosaic Quick Tour) and the Absolute Beginner’s Guide to Building Robots. He is currently working on a best-of collection of his writing, called Borg Like Me.


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Comments

  1. KNfLrPn says:

    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 says:

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

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