# Capacitor Values – Prefixes, Standards and Calculations

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 µF 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 as 0.000000000001

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

## 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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## 55 thoughts on “Capacitor Values – Prefixes, Standards and Calculations”

1. 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.

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

Oyvind

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2. 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.

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• Hi Evan,

R is resistance given in Ohms.
C is capacitance, given in Farads.

Cheers!
Oyvind

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• Think about it like filling a container with water. The capacitor stores electrons. A resistor in series with the capacitor will impede the flow, extending the time it takes to reach full capacity.

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

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• Hi,

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

Cheers!
Oyvind

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

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• No, there isn’t any minimum voltage.

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4. 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.

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• Hi Ricky,

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

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5. 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.

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• 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.

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• 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

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• 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?

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• Yes, exactly.

6. Then the table from rfcafe.com for?

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• 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.

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

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7. 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?

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• 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.

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8. 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!

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• In what context?

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

Best,
Oyvind

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9. 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

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• 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

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• 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

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• 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

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

10. 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?

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• 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

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11. 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

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

Best,
Oyvind

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12. … just reading through. Interesting

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• I took couple yrs of electronic engineering. .1/2
Back,25yrs ago as a technical student course my freshman/soph. Yr.
I really enjoyed electronics, never could afford all the highends and newer technology tht aspired thn…so the course helped me with tht, made a few dollars here and there as well as i was trying to fix every car stereo, with missing plug and solder my own pig out ..and burnt units.. (lack of sense, of most..) dollars was my lack so stayed close to those fools lol…amps were ALWAYS just a burnt curcuit…quik soldered jump wire and i was in there. I would b bumping to it same day…sry carried away for sec, i ended up going a whole nother direction.
For all my yrs, past few yrs started picking up flatscreens (tv) first couple nothing wrong, (prob jus ws n need of a reset) cause once booted up no sigins of anything. So ofcourse tht got the ball rolling again for me, i forgotten until tht moment tht i had ever heard words solder/flux/resistance. ..ac/dc lol smh well not all rest was so lucky as first (it my calling ibelieve) well starting back i didnt remember anything really, first few i spotted problems by merely eyes only, hot joints, burn tru, no standby voltage, fuse, dirty ribbon connections…buldging….not knowing where came from…started researching again to learn…i have been better with only my eyes…until i ran cross your charts, descriptions, and explanations…first and third person on delivering this complicated algebraic shockwaves of colors, numbers, letters, sy.bols, lol u have got me lined back up with a clear line of sight now….i was ready give my passion up again! Sry dnt know if im supposed to drop this here but i am did t want to lose ya and not share my story! Few of those past reads they seemed confused. ..but knew tht feeling to well, you are a gent and a scholar! ! Ty so, frm me and for thm….ur a good person for what udo here!!!! Thnx…

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

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14. i want to use a capacitor for my 125cc local motor cycle!!!
my batt is good and my regulator rectifier is good, but i install a 60w led light
1 as back up of my headlight 18w
and d other 2 is in d rear side
for increasing my illumination when i travel at night!
can i use capacitor for my 3 led light as a current smooth protection
and at d same time for helping my batt life…!
sir how to calculate of capacitance that i need in d future?
thank you very much
more power!!!
d name is Thomm
from d Philippines…

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15. Hi, what can I replace a 78 faret ceramic disc cap with? The application is in a tv power supply circuit. The value on the cap is u78Z .

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• Ceramic disc caps are very easy to find, so just replace it with another one.

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16. Hi please help! Let say I am required to select a capacitor value of 5.8nF for my circuit, but the only available capacitors in my workshop are 6.8nF and 4.7nF. Which value should i choose?

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• Hi, that depends on what it’s for. If you don’t know the calculations just pick one and see if it works. If it gives you a bad result, try the other one.

Best,
Oyvind

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17. Hon.Being inspried through your explanation,I am trying to
figure out as if we have a circuit
Of 220 volt supply AC and in circuit we need 50 volt DC in such a case how to find out required value capacitor like it’s
micro farade,it’s voltage rating,and if needed it’s charge.
How to calculate and figure out exact value capacitor we need?
CRJ.

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18. Hi ……

eeeeh am give Resistor as 100ohms , capacitor as 10ohms , inductor as 10ohms and de supply voltage is 200v ……plz help on hw to calculate de value of capacitor nd inductor …!!!

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19. Hello Oyvind,
I have a circuit board that I want to repair but 3 capacitors have blown and were taken out of the board so I have no reference.

Is there any way of knowing what capacitors I can use to get the board running?
No, I do not have a schematic.

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• There are ways to make a good guess at least. First of all – what type of circuit do the capacitor belong to?

A microcontroller circuit, connected to the power pin of the microcontroller? Often 100nF.

Connected to some kind of component with writings on them? Find the datasheet of the component and see if the datasheet tells you anything about its capacitors.

Best,
Oyvind

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20. If someone wanted to choose a capacitor for use as a DC blocker on a standard electric line, (120 VAC, 60HZ) in order for the capacitor to go bad before allowing the device to be damaged by, say lightning, but not restrict the incoming electricity during normal use, how would you choose the proper Farad rating in that case, as you couldn’t use the R*C multiplication, since there wouldn’t be a resistance in the line large enough to use the formula, correct?

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21. Hello Oyvind,

I want to use a capacitor in a simple circuit to blink a led by using a switch and a LED. Nothing else except a power supply of 5v from an arduino.
How can I calculate the value of the capacitor?
How can I use your formula in a DC supply? Is there still a frequency here and if yes how can I find it?

Thanks a lot,
Panos

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• Hi Panos, how to calculate the capacitor value depends on your circuit. I don’t see how you can blink an LED with just a switch (unless you’re planning to use a digital output from the Arduino with blinkled code). So if you can post a link to the circuit you’re planning to use, it would be easier to say.

Best,
Oyvind

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22. Hi love the stuff you have on the website. It really helped me a lot with understanding electronics.
I am making a pcb atm and have a question about capasitors.
I need to get from 220v AC to 5v dc and 3.3v dc.
Im using a 220v/5v 5w AC-DC converter to step down to 5 volts.
Then im putting a ams 1117 to step it down to 3.3 volt for my esp12f.
I want to use a capasitor to smooth the inflow off voltage to the esp12f.
How would i calculate the right size for this capasitor?
Or should i use something else to make the flow off voltage more even for the esp12f?
I would love to hear your thoughts or solutions to this problem.
Best regards,

Shermy

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• Hi Shermy,

You’ll find this information in the datasheet of the LM1117: https://www.ti.com/lit/ds/symlink/lm1117.pdf

On page 15 it says:
“A 10-μF tantalum on the input is a suitable input capacitor for almost all applications.”

On page 16 it says:
“The output capacitor is critical in maintaining regulator stability, and must meet the required conditions for both minimum amount of capacitance and equivalent series resistance (ESR). The minimum output capacitance required by the LM1117 is 10 µF, if a tantalum capacitor is used. Any increase of the output capacitance will merely improve the loop stability and transient response. The ESR of the output capacitor should range between 0.3 Ω to 22 Ω.”

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23. Please help me
How do I choose a new capacitor in a circuit cuz my radio capacitor just explode without me knowing the volt and the “uf” how to calculate to choose new capacitor

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• You have to start with the schematics of the circuit. Figure out the purpose of the capacitor. Then calculate the desired value for that purpose. If it’s a common circuit, this might be straightforward. If it’s a specially-designed circuit, it might be really difficult (unless you can get help from the designer)

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