Resistors

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Decoding Resistor Markings

Though they may not display their value outright, most resistors are marked to show what their resistance is. PTH resistors use a color-coding system (which really adds some flair to circuits), and SMD resistors have their own value-marking system.

Decoding the Color Bands

Through-hole, axial resistors usually use the color-band system to display their value. Most of these resistors will have four bands of color circling the resistor, though you will also find five band and six band resistors.

Resistors showing their stripes

Four Band Resistors

In the standard four band resistors, the first two bands indicate the two most-significant digits of the resistor's value. The third band is a weight value, which multiplies the two significant digits by a power of ten.

The final band indicates the tolerance of the resistor. The tolerance explains how much more or less the actual resistance of the resistor can be compared to what its nominal value is. No resistor is made to perfection, and different manufacturing processes will result in better or worse tolerances. For example, a 1kΩ resistor with 5% tolerance could actually be anywhere between 0.95kΩ and 1.05kΩ.

How do you tell which band is first and last? The last, tolerance band is often clearly separated from the value bands, and usually it'll either be silver or gold.

Five and Six Band Resistors

Five band resistors have a third significant digit band between the first two bands and the multiplier band. Five band resistors also have a wider range of tolerances available.

Six band resistors are basically five band resistors with an additional band at the end that indicates the temperature coefficient. This indicates the expected change in resistor value as the temperature changes in degrees Celsius. Generally these temperature coefficient values are extremely small, in the ppm range.

Decoding Resistor Color Bands

When decoding the resistor color bands, consult a resistor color code table like the one below. For the first two bands, find that color's corresponding digit value. The 4.7kΩ resistor shown here has color bands of yellow and violet to begin - which have digit values of 4 and 7 (47). The third band of the 4.7kΩ is red, which indicates that the 47 should be multiplied by 102 (or 100). 47 times 100 is 4,700!

Close-up of a 4.7kOhm resistor

4.7kΩ resistor with four color bands

If you're trying to commit the color band code to memory, a mnemonic device might help. There are a handful of (sometimes unsavory) mnemonics out there to help remember the resistor color code. A good one, which spells out the difference between black and brown is:

"Big brown rabbits often yield great big vocal groans when gingerly snapped."


Or, if you remember "ROY G. BIV", subtract the indigo (poor indigo, no one remembers indigo), and add black and brown to the front and gray and white to the back of the classic rainbow color-order.

Resistor Color Code Table

Image of 4, 5, and 6 band resistors and what each band stands for

Having trouble seeing? Click the image for a better view!

Resistor Color Code Calculator

If you'd rather skip the math (we won't judge!), and just use a handy calculator, give one of these a try!

Four Band Resistors

Band 1Band 2Band 3Band 4
Value 1 (MSV)Value 2WeightTolerance
   

Resistance:  1 kΩ ±5%

Five and Six Band Resistors

Note: Calculate your six band resistor here, but be sure to append the temperature coefficient to the final value of the resistor.


Band 1Band 2Band 3Band 4Band 5
Value 1 (MSV)Value 2Value 3WeightTolerance
   

Resistance:  1 kΩ ±5%

Decoding Surface-Mount Markings

SMD resistors, like those in 0603 or 0805 packages, have their own way of displaying their value. There are a few common marking methods you'll see on these resistors. They'll usually have three to four characters -- numbers or letters -- printed on top of the case.

If the three characters you're seeing are all numbers, you're probably looking at an E24 marked resistor. These markings actually share some similarity with the color-band system used on the PTH resistors. The first two numbers represent the first two most-significant digits of the value, the last number represents a magnitude.

Examples of E-24 marked SMD resistors

In the above example picture, resistors are marked 104, 105, 205, 751, and 754. The resistor marked with 104 should be 100kΩ (10x104), 105 would be 1MΩ (10x105), and 205 is 2MΩ (20x105). 751 is 750Ω (75x101), and 754 is 750kΩ (75x104).

Another common coding system is E96, and it's the most cryptic of the bunch. E96 resistors will be marked with three characters -- two numbers at the beginning and a letter at the end. The two numbers tell you the first three digits of the value, by corresponding to one of the not-so-obvious values on this lookup table.

CodeValue
CodeValue
CodeValue
CodeValue
CodeValue
CodeValue
01100
17147
33215
49316
65464
81681
02102
18150
34221
50324
66475
82698
03105
19154
35226
51332
67487
83715
04107
20158
36232
52340
68499
84732
05110
21162
37237
53348
69511
85750
06113
22165
38243
54357
70523
86768
07115
23169
39249
55365
71536
87787
08118
24174
40255
56374
72549
88806
09121
25178
41261
57383
73562
89825
10124
26182
42267
58392
74576
90845
11127
27187
43274
59402
75590
91866
12130
28191
44280
60412
76604
92887
13133
29196
45287
61422
77619
93909
14137
30200
46294
62432
78634
94931
15140
31205
47301
63442
79649
95953
16143
32210
48309
64453
80665
96976


The letter at the end represents a multiplier, matching up to something on this table:

LetterMultiplierLetterMultiplierLetterMultiplier
Z0.001A1D1000
Y or R0.01B or H10E10000
X or S0.1C100F100000


Resistors marked with E-96 codes

So a 01C resistor is our good friend, 10kΩ (100x100), 01B is 1kΩ (100x10), and 01D is 100kΩ. Those are easy, other codes may not be. 85A from the picture above is 750Ω (750x1) and 30C is actually 20kΩ.