There are some standard capacitor values that have developed over time. To find the value you need for your circuit you need to know how to deal with prefixes. And you need to know how to calculate capacitor values.

If you have looked for capacitors, you have probably seen many different letters and weird values. Like 0.47 or 22 pF. It is a bit confusing, but it’s easy to learn what it means.

In this article you will learn the most standard capacitor values, the prefixes used and how to calculate a capacitor value for your circuit.

## The Prefixes

Capacitor values are given in Farad. The symbol used is F. It’s named after the English physicist Michael Faraday.

But 1 Farad is pretty big. So capacitor values are usually given with a prefix. Often you are going to work with capacitors values in pico-farads to micro-farads.

To make this simpler to deal with, I’m going to show you how the prefixes work.

A prefix is something you put in front of the farad symbol (F). It tells you what you have to multiply the number with. For example 1 pF means 1 F multiplied with the prefix p which is 10^(-12). It can also be written 0.000000000001

Here is a table with the most common prefixes for capacitors:

Prefixes | ||
---|---|---|

1 Farad | ||

0.000001 Farad | ||

0.000000001 Farad | ||

0.000000000001 Farad | ||

## Which Capacitor Values Are There?

Capacitors are available in a lot of values. Over time, some standard values have emerged. Here is a table from rfcafe.com with the most commonly found capacitor values:

## How Do You Choose Capacitor Values?

You choose a capacitor value by using the RC time constant:

This constant gives you the time it takes for a voltage in an RC circuit to go from 0% to 63% of its full value.

You can use this time constant to calculate the cutoff frequency in a filter, or just how long a delay will be in a blinking light circuit.

## Calculating Capacitor Value For A Circuit

Let’s say we want to make a low pass filter with a cutoff frequency of 15 kHz. The formula for calculating cutoff frequency is:

and by switching it around we can calculate for C:

Now, let’s choose to use a 1k resistor. This gives us:

So to get a cutoff frequency of 15 kHz, we need a 1k resistor and a 11 nF capacitor.

## Different Types of Capacitors

To make everything more confusing, capacitors come in many different types. I have written a simple guide on how to choose a capacitor type that you should check out.

There is no need to memorize these things. Just bookmark this page and you’ll have easy access to it later on. When you have used the prefixes and the formula enough times, you will automatically remember them.

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Jonathan says

Hey Oyvind,

I am trying really hard to understand what’s on the page, but it’s really hard to when all the pictures aren’t loading. I don’t know what’s happening. It only happens on this one.

admin says

Hmm. that’s weird. They are loading for me…

Oyvind

Evan says

Hello there Oyvind,

I was wondering about the RC time constant. What is R and what is C? So far capacitors really have me confused about whats what.

admin says

Hi Evan,

R is resistance given in Ohms.

C is capacitance, given in Farads.

Cheers!

Oyvind

Sapna Razdan says

if i need a 400V capacitor, can i use 350V or 450V capacitor instead of 400V.

admin says

Hi,

400 volt is how much voltage the capacitor can handle. So you want 450V at least.

Cheers!

Oyvind

George Constanza says

Is there a minimum value of voltage that a capacitor can work with?

admin says

No, there isn’t any minimum voltage.

Ricky Ho says

Hi.

I would like to introduce the application of a capacitor to the kids and I think a simple windmill project should be the best example to highlight the application.

I need a small capacitor in a simple electric circuit of a self-made windmill. I am going to use 2 x 1.5v battery for the project. Appreciate your advise on what type of capacitor to use for this project as I do not know how to choose one. Thank you.

admin says

Hi Ricky,

It’s difficult to say without knowing more. What is the purpose of the capacitor in this application?

Barry Ng says

Hi, I seriously don’t know what page mean can you give a simpler explanation of all his page means like starting from the prefixes and the calculation.

Barry Ng says

Hi , sorry about the typo above. I was saying that can you give me a simpler explanation at this page I don’t understand what the prefixes and the calculation means.

admin says

Hey Barry,

Prefixes are an shorter way to write numbers. For example “kilo” means 1000 and uses a “k” as a symbol. This means instead of writing 10000, I can write 10k.

Best,

Oyvind

Barry Ng says

What is the table from rfcafe.com for? And what is the use of knowing this? Is it if we know how to calculate then we know which capacitor will be the best in our circuit?

admin says

Yes, exactly.

Barry Ng says

Then the table from rfcafe.com for?

admin says

It shows the most commonly found capacitor values. If you for example have calculated that you need a capacitor of 17µF, you can check if that exists in the table. Since it doesn’t you have to find another way of doing it or go with one of the values that are listed.

Barry Ng says

Tq

Barry Ng says

Can I know what is the symbol equal to R * C? And please explain what it mean.

Leo says

Hi, can I know the part of “how do you choose capacitor values” in this page. What is the equation of that first symbol before equal R times C? And also explain what did it mean? Is it voltage?

admin says

It’s called “tau”. It’s the time constant. This constant gives you the time it takes for a voltage in an RC circuit to go from 0% to 63% of its full value.

Ibn Ishaq says

please can you explain what cut off frequency means.i tried google searching but i got confused even more.

i love your writing style though….keep up the good work!

admin says

In what context?

In a low-pass filter for example you only allow frequencies below the cutoff frequency to go through.

Best,

Oyvind

Billy says

Hi, in your exemple, how did you end up with 15 000Hz that’s the only part I don’t get. I don’t know what a low-pass filter is could you explain?

Thanks

Billy says

I’m asking because I want to make a hand crank flashlight using a 6V and 0.04A Dynamo, 3,1V LEDs, an interupter/switch and a capacitor but I don’t know which capacitor to choose. So I would like to figure it out.

Thanks

admin says

Hi Billy,

For your project, you don’t need a low-pass filter, so just ignore that part.

It’s hard for me to say anything about the size you need since I don’t what you are using the capacitor for.

Best,

Oyvind

Billy says

I need a capacitor to store the energy from my dynamo. Does that make sense? I want to be able to use my flashlight without having to continusly rotate the motor. Just like hand crank flashlights that we can purshase. (Its doesn’t have to be as efficient though)

Thanks

admin says

Ah ok, I understand. Capacitors normally store very little energy. But you should look into super capacitors. They can store more energy.

Philip B says

I’m trying to repair the power supply circuit in a transceiver that I have. I know I need a 3300 uF 70 VDC electrolytic capacitor, but every time I go to a website to FIND one, I’m also asked what tolerance I need, ripple current, ESR, ROHS compliant,etc. Do I need to worry about these values or not?

admin says

Hey Philip,

The most important for you is to find a capacitor that has 3300 µF and a voltage rating of 70V or more. Don’t worry about the other stuff.

Best,

Oyvind

Zeljko Vukosavljev says

Hi,

if I want LED 3V blinking once per second, using this scheme, but the input voltage is 9v, what are the values for R and C. If you can write formulas and how you got those results. Thank you.

Zeljko

admin says

Hi,

I don’t know which circuit you are referring to. There are no blinking LEDs in this article..

Best,

Oyvind

Zeljko Vukosavljev says

Hi,

I think the circuit from the text above, if I put on the output LED 3V and input voltage of 9V.

admin says

Do you mean the filter circuit? It will not make the LED blink. Here’s some circuits to blink an LED:

http://www.build-electronic-circuits.com/blinking-led-circuit/

Best,

Oyvind

Zeljko Vukosavljev says

OK, thanks.

Zeljko

Fabricio baca says

… just reading through. Interesting

MD. Rakibul Islam Prince says

suppose I am using a 24v DC power supply.then as a decoupling capacitor which capacitance/volt

should I use?