# Is my inductor really 22µH?

I have a package of 10 inductors, all of which are supposed to be 22µH, but they all have "220" printed on the case. It does not seem right when I compare to an otherwise identical (same type) inductor with an inductance of 3.3µH, which has "3R3" printed on it. Is it just odd ordering or am I missing something? Inductor is an SDR0604 type.

• I don't get it, what else would you expect the marking "220" to mean? In most electronics contexts it means 22. Mar 1, 2011 at 22:26
• @Nick T, given that the other one was "3R3" I'd expect "220" to mean "220R" or 220µH. Mar 1, 2011 at 22:28
• Maybe it's 22 Henries. Were the inductors delivered with a forklift? Mar 2, 2011 at 1:44
• With +/-5% components, all you need are 2 digits plus one for order-of-magnitude. Just like on resistors and capacitors, there are 2 mantissa digits and one for radix. Mar 2, 2011 at 3:10
• MEasure them. It's the only way to know. Mar 2, 2011 at 7:32

That should be read as 22 × 100 µH and 3.3 µH respectively. The R is a decimal, the last digit otherwise is an exponent.

There are two ways of marking parts...

A Three digit code for values from 10 and up

X Y Z
X - First digit
Y - Second digit
Z - Power of ten

220 would be 22 = 22 x 10^0 (1)
221 would be 220 = 22 x 10^1 (10)
222 would be 2,200 = 22 x 10^2 (100)
223 would be 22,000 = 22 x 10^3 (1000)


The Minimum for this coding would be 100 = 10 x 10^0 and the Maximum would be 999 = 99,000,000,000 = 99 x 10^9 (1,000,000,000)

For values under 10

you use a character to replace the decimal point

e.g. 3R3 = 3.3 R33 = 0.33

R is used for Ohms.

For resistors the value is usually in Ohms For Capacitors the value is usually in pico farads

e.g. a Capacitor marked 103 would be 103 pF = 10 x 10^3 (1000) pF = 10nF = 0.01uF

For Inductors the value is usually in micro henrys e.g. a Inductor marked 220 woulf be 22uH = 22 x 10^0 (1) uH

The part marked 3R3 is a 3.3 ohm resistor as R is used on resistors.

• I think "R" can be used on inductors too, but I have no idea why they use that convention. Maybe "L" wouldn't be clear enough; suppose it could be read as a 7 upside down... Mar 1, 2011 at 22:34
• Why couldn't they just write 22 µH as "22"? Mar 2, 2011 at 16:11
• @Wonko The Sane: You say the minimum for this coding is 100 (meaning 10 x 10^0 = 10)... but why can't you have 010 (meaning 01 x 10^0 = 1)? Mar 2, 2011 at 16:14
• @BG100: If you did that then you lose significant digits as you're putting useless leading zeros in your mantissa (significand). How would you express 1.5, or 3.3 as in the OP question? Mar 2, 2011 at 16:40
• @endolith "I suffered for my knowledge, now it's your turn" Sep 25, 2012 at 19:47

220 means that the value is 22 times 10^0, or 22uH. It's a similar notation to that used for small value capacitors. If they were really 220uH they would have the value 221.

Panasonic SM inductors use R in the part marking (for example, 2R6 corresponds to the 2.6 microhenry part on the specified datasheet).