# why 4.7uf and not 5uf?

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Hi guys,

A curious question someone here might be able to answer...

why is that there is are 4.7uf or 2.2uf or 1.6uf etc values of capacitance
and not rounded values of say 5uf, 2uf, etc?

why those values 47, 22, 16, etc....?? is there something special about
them??

love to hear an reason for using those figures.

Re: why 4.7uf and not 5uf?

Google is your friend. Look for preferred values.

Re: why 4.7uf and not 5uf?

"KD"

**  When 6 steps in value make up a decade ( ie 10 times) increase in value.

So each step needs to be the 6th root of 10.

10 exp 0.1666  =   1.468

The exact steps then are:

1,  1.47,   2.15,   3.16,   4.64,   6.81,  10.

Rounded to :

1,  1.5,  2.2,  3.3,  4.7,  6.8,  10.

For 12 steps,  the number are:

1,  1.21,  1.47,  1.78,  2.15,  2.61,  3.16,  3.83,  4.64,  5.62,  6.81,
8.25,  10.

.........   Phil

Re: why 4.7uf and not 5uf?

Phil,

Your knowledge amazes me!

Jackie

capacitance
value.

Re: why 4.7uf and not 5uf?

This is were the E6 and E12 range comes in

e.g. E6 range has 6 values per decade

Phil,

Your knowledge amazes me!

Jackie

capacitance
value.

Re: why 4.7uf and not 5uf?

"Jackie"

**  Yeah  -  so I can use a "scientific" pocket calculator.

BTW

Do YOU  know what is the same as the 12th root of 2 ?

.............   Phil

Re: why 4.7uf and not 5uf?

I'm sure this is a loaded question! - No I don't

Jackie

6.81,

Re: why 4.7uf and not 5uf?

Maybe not, one answer I can think of is a semitone.  A semitone is the
difference in pitch between each fret on the guitar or practically any
musical  instument that is tuned to what is called a "chromatic scale"
(aka equal tempered 12 note scale).  Musical tones are measured in
semitones and octaves where as electrical component values are
normally measured in decades and as Phil pointed out.

regards,
Johnny.

Re: why 4.7uf and not 5uf?

"Johnny"
"Jackie"

**  Spot on.

**  That is the connection.

Eg:  a " third octave" audio equaliser has steps that are governed by the
3rd root of 2.

.........   Phil

Re: why 4.7uf and not 5uf?

Amazing!.. Thank you Phil!..

So why 6 steps in value value make up a decade? (Why 6?)

Re: why 4.7uf and not 5uf?

"Posun Hurla"

**  Think about tolerace percentages:

20 %,  10 % ,  5 %,  2%    etc.

6 steps makes good sense when the allowable tolerance is +/- 20 %.

..........   Phil

Re: why 4.7uf and not 5uf?

when i was a lad,,,,,,,,   2.5uF 5uF 7.5uF was the go.
with electro caps near enough is good enough anyway.

E3 are the most used values ie; 3 values per decade:
1, 2.2, 4.7, 10, 22, 47 etc