SMD Resistor Coding

SMD Resistors are usually coded with a numerical equivalent of the familiar three band colour code. In the same way as wire ended components, precision resistors (1% or better) may be marked with a four digit code.

The first two (or 3) digits are the first two (or 3) digits of the resistance in ohms, and the third(or 4th) is the number of zeros to follow - the 'multiplier'.

Resistances of less than 10 ohms have a 'R' to indicate the position of the decimal point.

Some examples will meake this clearer: 

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 49.9 kohm
683 is 68 000 ohms, or 68 kohm	16234 is 162 000 ohms, or 162 kohm
105 is 1 000 000 ohms, or 1 Mohm	0R56 or R56 is 0.56 ohms
8R2 is 8.2 ohms

 

---

But just to make life more interesting, 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	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 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 (49.9 k) and 43E a 2740000 (2.74 M). This marking scheme applies to 1% resistors only.

---

A similar scheme can be used for 2, 5 and 10% tolerance types. The multiplier letters are identical to the 1% ones, but occur before the number code. Just to make it even more fun, a different coding scheme is used. Here it is:

2%						5%						10%
code	value		code	value		code	value		code	value		code	value
01	100		13	330		25	100		37	330		49	100
02	110		14	360		26	110		38	360		50	120
03	120		15	390		27	120		39	390		51	150
04	130		16	430		28	130		40	430		52	180
05	150		17	470		29	150		41	470		53	220
06	160		18	510		30	160		42	510		54	270
07	180		19	560		31	180		43	560		55	330
08	200		20	620		32	200		44	620		56	390
09	220		21	680		33	220		45	680		57	470
10	240		22	750		34	240		46	750		58	560
11	270		23	820		35	270		47	820		59	680
12	300		24	910		36	300		48	910		60	820

So with this scheme, A55 is a 330 ohm, 10% tolerance resistor, C31 a 5%, 18000 ohm (18 kilohm) unit, and D18 510000 ohms (510 kohm) 2% tolerance.

Personally, I'd check with an ohm-meter!

last updated 10 April 2003 by G4PMK