Reading a Resistor's Value
Through-hole (PTH) Axial Resistor Colored Bands
Axial resistors, the kind that is most often used when prototyping, have color coded bands that specify the resistance value and tolerance of the resistor. They usually come in 4 or 5 band flavors, with 5 band resistors being more precise.
To read a banded resistor, align it so that the three (or four) closely spaced bands are on the left, and the furthest spaced band is on the right. Then, use the following chart to determine the values from left to right:
The first 2 (or 3 bands, on a 5-band resistor) specify the resistance value, and the 3rd (or 4th) specify the magnitude multiplier.
Sample Reading
For example, the resistor shown above has the following values:
- Brown =
1
- Blue =
6
- Black =
0
- Orange =
1k
Magnitude Multiplier - Gold =
5%
Tolerance
Therefore, the resistor has 160Ω * 1k = 160kΩ
, with a tolerance of ±5%
.
Surface Mount (SMD)
There are 2 primary methods of labeling SMD resistors.
The first uses 3 numbers such as 424
, this can be understood as 42 104 = 42 x 10,000 = 420kΩ
. If the resistor were labeled as 420
it would be 42 100 = 42 * 1 = 42Ω
.
The second method, EIA Standard, uses 2 numbers and a letter such as 66B and this will require the tables below to decode.
The numbers are a lookup code.
CODE | Value | CODE | Value | CODE | Value | CODE | Value | |||
---|---|---|---|---|---|---|---|---|---|---|
01 | 100 | 25 | 178 | 49 | 316 | 73 | 562 | |||
02 | 102 | 26 | 182 | 50 | 324 | 74 | 576 | |||
03 | 105 | 27 | 187 | 51 | 332 | 75 | 590 | |||
04 | 107 | 28 | 191 | 52 | 340 | 76 | 604 | |||
05 | 110 | 29 | 196 | 53 | 348 | 77 | 619 | |||
06 | 113 | 30 | 200 | 54 | 357 | 78 | 634 | |||
07 | 115 | 31 | 205 | 55 | 365 | 79 | 649 | |||
08 | 118 | 32 | 210 | 56 | 374 | 80 | 665 | |||
09 | 121 | 33 | 215 | 57 | 383 | 81 | 681 | |||
10 | 124 | 34 | 221 | 58 | 392 | 82 | 698 | |||
11 | 127 | 35 | 226 | 59 | 402 | 83 | 715 | |||
12 | 130 | 36 | 232 | 60 | 412 | 84 | 732 | |||
13 | 133 | 37 | 237 | 61 | 422 | 85 | 750 | |||
14 | 137 | 38 | 243 | 62 | 432 | 86 | 768 | |||
15 | 140 | 39 | 249 | 63 | 442 | 87 | 787 | |||
16 | 143 | 40 | 255 | 64 | 453 | 88 | 806 | |||
17 | 147 | 41 | 261 | 65 | 464 | 89 | 825 | |||
18 | 150 | 42 | 267 | 66 | 475 | 90 | 845 | |||
19 | 154 | 43 | 274 | 67 | 487 | 91 | 866 | |||
20 | 158 | 44 | 280 | 68 | 499 | 92 | 887 | |||
21 | 162 | 45 | 287 | 69 | 511 | 93 | 909 | |||
22 | 165 | 46 | 294 | 70 | 523 | 94 | 931 | |||
23 | 169 | 47 | 301 | 71 | 536 | 95 | 953 | |||
24 | 174 | 48 | 309 | 72 | 549 | 96 | 976 |
The letter serves as a multiplier against the values above.
Letter | Multiplier |
---|---|
Z | 0.001 |
Y/R | 0.01 |
X/S | 0.1 |
A | 1 |
B/H | 10 |
C | 100 |
D | 1 000 |
E | 10 000 |
F | 100 000 |
So, that 66B has a value of 475
in the first table and a multiplier of 10 from the second table, which would be 475 * 10 = 4,750Ω
.