Why is 4.7 a standard value in electronics?

Question

You always see 4.7K resistors, 4.7uF capacitors, and such. Since 47 is a prime number, this seems very odd (pun intended). Why 47 and not, say, 48 or 50?

Answer 1

I think it's because there is a 'relatively' constant ratio of "standard values" from 1 to 10 ... and from 10 to 100
etc

10
15
22
33
47
68
100 .... note that each value is approx 1.5 times the previous value ... respecting the number of signif digits leads to "47" being one of these values.

Since there are 6-values in this scale, it is called the
"E6" scale

E12 goes:
10
12
15
18
22
27
33
39
47
56
68
82
100

"47" also appears in the "E12 scale of values",
each being apprx 1.2 = apprx squareroot of 1.5 ...

I point out the 47 appears in the E24 scale as well, but
NOT in the E48 scale .. where the 'standard values'
jump from 464 to 487 ....

and NOT in the E96 scale

but 47 returns in the E192 scale

Answer 2

As Stewart H pointed out, those values are based on a ±20% tolerance of part value. That used to be the standard tolerance for resistors, and still is for many capacitors. Nowadays, ±10%, ±5% and ±1% resistors are common, and if you look at a table of values for a ±1% resistor, you will find many more values available than those "standard" numbers.

Answer 3

There are in fact different sets of preferred values for different component tolerances. To give an example of the rational, if we start with a 1ohm resistor manufactured to a +/-20% tolerance, the upper value is 1.2ohms. The next value up is 1.5ohms giving a lower value of 1.2ohms and an upper value of 1.8ohms. The other values are 2.2, 3.3, 4.7, 6.8.

The values are actually on a logarithmic scale and are different for different tolerances.

Answer 4

ya know that's a pretty good question. 4.7 isn't the only common value for resistors and such. other values for resistors are:
1.0, 1.2, 3.3, and 5.6... now i'm curious about that...

Answer 5

Sony makes chips witha certain range of power of 4.7 watts