SMT Resistors Coding

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.

For example: 334 is written on the Top of 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 written 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
or 22 and no zero's = 22R or 47 and no zero's = 47R. Sometimes the resistor is marked: 10, 22 and 47 to prevent a mistake.
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.

Here are some examples:

Three Digit Examples	Four Digit Examples
330 is 33 ohms - not 330 ohms	1000 is 100 ohms - not 1000 ohms
221 is 220 ohms	4992 is 49 900 ohms, or 49k9
683 is 68 000 ohms, or 68k	1623 is 162 000 ohms, or 162k
105 is 1 000 000 ohms, or 1M	0R56 or R56 is 0.56 ohms
8R2 is 8.2 ohms

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.

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	267		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 as follows:

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) to make sure.

Chip resistors come in the following styles and ratings:
Style: 0402, 0603, 0805, 1206, 1210, 2010, 2512, 3616, 4022
Power Rating: 0402(1/16W), 0603(1/10W), 0805(1/8W), 1206(1/4W), 1210(1/3W), 2010(3/4W), 2512(1W), 3616(2W), 4022(3W)
Tolerance: 0.1%, 0.5%, 1%, 5%
Temperature Coefficient: 25ppm 50ppm 100ppm