Highfields Amateur Radio Club
Constructors Corner.


Resistor Identification Codes.
By Brian, MW0GKX.

When constructing electronic projects or repairing faulty items it will be necessary to determine the exact value of resistors, which are colour coded. I have put together this page for Resistors and this page for Capacitors to help identify their values.

Resistors with 4 coloured bands

For traditional resistors there are usually FOUR coloured bands. The first three bands will show the value of the resistor (the resistance) in Ohms. The fourth coloured band indicates the tolorance of the resistor, that is how close the actual resistance may be to the value indicated. A 1k Ohm (1000 Ohm) resistor with a 20% tolorance could have a value anywhere between 800 and 1200 Ohms.

The tolorance band is sometimes spaced further apart from the other three bands, which helps when deciding which way round to read off the value, which is sometimes difficult to establish immediately.

FIRST DIGIT
First Colour Band
 SECOND DIGIT
Second Colour Band
 MULTIPLIER
Third Colour Band
BLACK
 0
0
x 1
BROWN
 1
1
x 10
RED
 2
2
x 100
ORANGE
 3
3
x 1,000
YELLOW
 4
4
x 10,000
GREEN
 5
5
x 100,000
BLUE
 6
6
x 1,000,000
VIOLET
 7
7
x 10,000,000
GREY
 8
8
x 100,000,000
WHITE
 9
9
x 1,000,000,000

TOLORANCE
Fourth Colour Band:
BROWN
1%
 RED
5%		 GOLD
5%		 SILVER
10%		 SALMON
20%

Examples:
BROWN BLACK BROWN SILVER = 100 Ohms (Usually expressed as 100R) 10% Tolorance.
YELLOW VIOLET RED GOLD = 4700 Ohms (Usually expressed as 4.7K) 5% Tolorance.
ORANGE ORANGE YELLOW SILVER = 330000 Ohms (Usually expressed as 330K) 10% Tolorance.

Resistors with 5 coloured bands

A number of resistors have FIVE coloured bands to indicate their resistance value and tolorance. The first four bands indicate the value while the fifth band indicates the tolorance.  Again it is often difficult to tell which way round to read off the value, but the tolorance band is usually spaced a little further apart from the first four bands.
FIRST DIGIT
First Colour Band
 SECOND DIGIT
Second Colour Band
 THIRD DIGIT
Third Colour band
 MULTIPLIER
Fourth Colour Band
BLACK
 0
0
0
x 1
BROWN
 1
1
1
x 10
RED
 2
2
2
x 100
ORANGE
 3
3
3
x 1,000
YELLOW
 4
4
4
x 10,000
GREEN
 5
5
5
x 100,000
BLUE
 6
6
6
x 1,000,000
VIOLET
 7
7
7

GREY
 8
8
8
 GOLD
 x 0.1
WHITE
 9
9
9
 SILVER
 x 0.01

TOLORANCE
Fifth Colour Band:
BROWN
1%
RED
2%
GOLD
5%
SILVER
10%

Examples:
BROWN BLACK BLACK BLACK SILVER = 100 Ohms (100R) 10% Tolorance.
YELLOW VIOLET BLACK BROWN GOLD = 4700 Ohms (4.7K) 5% Tolorance.
ORANGE ORANGE BLACK ORANGE SILVER= 330000 Ohms (330K) 10% Tolorance.

Surface Mount Resistors Codes.

All SM resistors conform to a 3-digit or 4-digit code. But there are a number of codes, according to the tolerance of the resistor. It's getting very complicated. Here is a basic 3-digit SM resistor:

The first two digits represent the two digits in the answer.
The third digit represents the number of zero's you must place after the two digits.
The answer will be OHMS.

For example: 334 is 33 0 000. This is written 330,000 ohms. The comma can be replaced by the letter "k". The final answer is: 330k.

222 = 22 00 = 2,200 = 2k2

473 = 47 000 = 47,000 = 47k
105 = 10 00000 = 1,000,000 = 1M = one million ohms.

There is one trick you have to remember. Resistances less than 100 ohms are written: 100, 220, 470.
These are:

10 and NO zero's = 10 ohms = 10R
22 and no zero's = 22R
47 and no zero's = 47R.
Sometimes the resistor is marked: 10, 22 and 47 to prevent a mistake.

'0000' (or sometimes just '0') is a value on a surface-mount resistor. It is a zero-ohm LINK!

Resistances less than 10 ohms have 'R' to indicate the position of the decimal point.
Remember: R = ohms, k = kilo ohms = 1,000 ohms, M = Meg = 1,000,000 ohms.
The 3 letters (R, k and M) are put in place of the decimal point. This way you cannot make a mistake when reading a value of resistance.

A new coding system has appeared on 1% types. This is known as the EIA-96 marking method. It consists of a three-character code. The first two digits signify the 3 significant digits of the resistor value, using the lookup table below. The third character - a letter - signifies the multiplier.

1% EIA-96
code value   code value   code value   code value   code value   code value
01 100 17 147 33 215 49 316 65 464 81 681
02 102 18 150 34 221 50 324 66 475 82 698
03 105 19 154 35 226 51 332 67 487 83 715
04 107 20 158 36 232 52 340 68 499 84 732
05 110 21 162 37 237 53 348 69 511 85 750
06 113 22 165 38 243 54 357 70 523 86 768
07 115 23 169 39 249 55 365 71 536 87 787
08 118 24 174 40 255 56 374 72 549 88 806
09 121 25 178 41 261 57 383 73 562 89 825
10 124 26 182 42 237 58 392 74 576 90 845
11 127 27 187 43 274 59 402 75 590 91 866
12 130 28 191 44 280 60 412 76 604 92 887
13 133 29 196 45 287 61 422 77 619 93 909
14 137 30 200 46 294 62 432 78 634 94 931
15 140 31 205 47 301 63 442 79 649 95 953
16 143 32 210 48 309 64 453 80 665 96 976

The multiplier letters are :

letter mult   letter mult
F 100000 B 10
E 10000 A 1
D 1000 X or S 0.1
C 100 Y or R 0.01

22A is a 165 ohm resistor, 68C is a 49900 ohm (49k9) and 43E a 2740000 (2M74). This marking scheme applies to 1% resistors only.

A similar arrangement can be used for 2% and 5% tolerance types. The multiplier letters are identical to 1% ones, but occur before the number code and the following code is used:

2%   5%
code
value
  code value
code
value
  code value
01 100 13 330 25 100 37 330
02 110 14 360 26 110 38 360
03 120 15 390 27 120 39 390
04 130 16 430 28 130 40 430
05 150 17 470 29 150 41 470
06 160 18 510 30 160 42 510
07 180 19 560 31 180 43 560
08 200 20 620 32 200 44 620
09 220 21 680 33 220 45 680
10 240 22 750 34 240 46 750
11 270 23 820 35 270 47 820
12 300 24 910 36 300 48 910

With this arrangement, C31 is 5%, 18000 ohm (18k), and D18 is 510000 ohms (510k) 2% tolerance.
Always check with an ohm-meter (a multimeter) if you are unsure.

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