Three digit codes (Capacitor codes)

Posted by on January 30, 2011

This is just a quick note on how to read them, it seems as if many people struggle with this but as far as you’re concerned the only thing that matters is getting the actual value in a meaningful unit (farads!) so let’s see how we can interpret those three digit codes rather easily!

A few example codes:

Enlightenment:

Imagine you’ve got a capacitor marked “104” I could tell you it’s value is 100nF, but how did I reach to this conclusion?, simple — The last number on the code is the actual multiplier!

For instance:

And so on.

So if we take the first two numbers and we simply “add N amount of zeros” we reach the actual value of the capacitor in picofarads.

Example: 423 = 42000pF, we know therefore this is a 42nF capacitor.

But what about the letters?

They represent a tolerance range!

Not surprisingly the most common tolerance, specially when it comes to ceramic ones is K (more or less 10%) — This means a capacitor marked 104K will exhibit a value in the range of 90 to 110nF.

It’s also important to know that different types of capacitors display different properties, some are more microphonic than others, some are stable over a wide range of temperatures; others are not, etc. Which is why it’s important to pay close attention to them, specially when it comes to RF, audio, and any other sensitive application.

I know what you’re thinking!

What happens under 100pF ? how are they marked ?

That’s simple, there’s no need to add a multiplier under this range, so 100 would actually mean 10pF, 200 would mean 20pF, etc.

It is however possible that a capacitor marked “90” be 90pF. If the code is not three digits long you can assume the value is given in picofarads. Otherwise you may use a capacitance meter to make sure.

Just keep in mind that measuring such low capacitances requires a correctly calibrated meter, if you’re using a LCR meter try not to use external leads, instead plug the capacitor directly onto the test unit. Worst case scenario, use the relative function to null out any parasitic capacitances.

That’s it.

Now you know how to read the three digit codes and we didn’t even have to venture into (spooky music) “maths”.

Cheers!