noob questions about the values of capacitor - same but different...?

[Snufkinoob]

I'm going to have a go at building a fuzz circuit but before I order parts, one thing is confusing me about capacitor values. I've done some searching and reading but couldn't find anything, so I hope this isn't an often-posted question. 

Basically, the list of cap values I'll need have been written with different units of value, for example:

0.1uF
0.022uF
56pF

Is there a specific reason for this mix of uF and pF?

I can find caps to buy online that technically have the same value, just not written the same as on the list.

For example, could the 0.22uF be replaced by a 22nF cap for example since that's essentially the same thing.
Or if a Cap is listed as 0.0022uF could I just use one designated as 2.2nF or 2200pF at the store (assuming that's the right conversion) etc.

I'm just getting the hang of the whole uF,nF, pF, scale, but I hope that makes sense.

Or is specific use of uF,nF, pF done for a specific reason? 

Thanks

[greaser_au]

In this case the units are very much interchangeable (with the proper scaling),  like 0.1m, 1dm,  10cm,  or 100mm (all the same measurement with a different prefix).  
It's just (in)convenience to use different prefixes. if the world was properly organised we'd all be using simple-to-use SI units, but some countries still have stock of the 0.002MFD and 2000PFD  capacitors, so they use non-scientific notation...  

Proper use would be to go no higher than xxx, and no lower than x.x before switching to the next prefix (though uf is the 'largest conventional unit' for caps - it's unusual to see millifarads). e.g:
220uF, 22uF, 2.2uF, 220nF, 22nF, 2.2nF, 220pf etc.

david

[lightcycle]

If the caps you found have technically the same value, just written in another way, then you can use them. 0.0022uF is exactly the same value as 2.2 nF and 2200 pF. Just as 1 kiloohm could be written as 1000 ohm instead, or 0.2 Ampere could be written as 200 milliAmpere instead. Note however in the example you gave that 0.22 uF would be 220 nF.

[Snufkinoob]

Thought so. Excellent, thanks.

I'll be double-checking all the values too. Thanks for pointing out my error.

[thelonious]

Here's a chart I found helpful when I was starting out: http://www.justradios.com/uFnFpF.html

And here's a capacitor number code interpreter from Jack O: http://www.muzique.com/schem/caps.htm

[Snufkinoob]

That'll come in handy, thanks.

[Hemmel]

Also maybe worth noting, use of "uF" is because it's faster to type than "µF". "µ" (or "Mu" in Greek) is the symbol for "micro".
On a PC keyboard depending on your OS locale, you can type that character by pressing "AltGr+M" (AltGr being on the right of the spacebar). I don't know for Mac keyboards.
So "uF" or "µF" stands for "microFarad".
"nF" for nanoFarad and "pF" for picoFarad.

[induction]

Also worth noting, some cap manufacturers use 'M' or 'm' for micro. So instead of 1u or 1µ, you'll see 1M or 1m.

It's like they hate the metric system and are trying to destroy it from the inside.

[thelonious]

On Mac, µ is Option+M

[PRR]

> For example, could the 0.22uF be replaced by a 22nF cap for example since that's essentially the same thing.

0.22uFd is _220_nFd. Not 22. (Ah-- Markus caught this.)

> Is there a specific reason for this mix of uF and pF?

Caps cover a million-million to one range.

The power-filter for a boom-car sound system is 1,000,000,000,000pFd. It is easier to say "1Fd".

A tweak-cap in a radio might be 0.000,000,000,01Fd. It is easier to say "10pFd".

Decades back there was only uFd (usually spelled mFd) and its tiny brother mmFd (what we now call pFd). And a One Farad capacitor was unheard-of (except when playing pranks on new kids). Someone decided that 0.002uFd was too awkward and invoved nFd.

[Beo]

I like use of uF, nF and pF. It makes for clean readable schematics, avoiding decimals. Which reminds me, you may see notations like 4k7 for resistors and 1n5 for capacitors. This means 4.7kohms or 4700ohms, and 1.5nF or 1500pF respectively. Again, avoiding decimals and making for nice schematic notation.

[Jdansti]

The easiest way for me to convert the units is by moving the decimal place by 3 places and knowing that pf < nF < μF.

For example, it takes "more" pF to make a nF because pFs are smaller than nFs (by convention).

1000pF = 1nF       1pf = 0.001nF     

1000nF = 1μF      1nF = 0.001μF

All I'm doing is moving the decimal place three places one way or the other, which is the same as multiplying or dividing by 1000.

If I want to convert 0.068μF to nF, I know that the number I end up with will be a larger number than 0.068 because it takes more nF to make a μF.  I move the decimal place 3 places to the right to make a bigger number and end up with 68nF.
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Or as my HS physics teacher taught us the longhand way.

Say I want to convert 0.22μF to XnF.

0.22μF = XnF

I multiply by 1000nF/1μF because 1000nF/1μF equals "1". You can multiply any number by 1 and not change the number.

0.22μF x 1000nF = XnF
              1μF

Now the μF units on top and bottom cancel out leaving only nF units.

0.22μF x 1000nF = XnF
                1μF

This leaves:
0.22 x 1000nF = 220nF