How to read resistor code

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Useful links: 

• How to read resistor code
• How to read capacitor code
• How to do soldering

How to read resistors code ? 

Almost every electronics website in this world has a page for teaching how to read resistor codes :). We are not going to write the same article again. Instead, we are going to share links to sites which teach you have to read a resistor code.

The following image should make you clear, however, please check the links below, if you do not understand the image below:

Links:

1. Digikey: Digikey has an online resistance value calculator. Most of the electronics people use 4 band carbon film resistors, so, this calculator should be very helpful for you.
2. Instructables: This tutorial has given a resistors color code chart, some example and some exercises. This is good !
3. WIKIHOW: This tutorial has real pictures to teach you how to read resistors. It should help you.
4. Hobby-hour: Hobby hour has gone a bit further. It has written a lot about 4 band and  5 band resistors. In addition, it has written about different tolerances and series of resistors. Recommended !

The video below is also very useful: 

Source: Sparkfun.com

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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.

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.

Here’s a table of each of the colors and which value, multiplier or tolerance they represent:

Here’s an example of a 4.7kΩ resistor with four color bands:

When decoding the resistor color bands, consult a resistor color code table like the one above. For the first two bands, find that color’s corresponding digit value. The 4.7kΩ resistor 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!

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:

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.

Color Code Calculator

If you’d rather skip the math (we won’t judge :), and just use a handy calculator, give this a try!

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.

In the above example picture, resistors are marked 104, 105, 205, 751, and 754. The resistor marked with 104 should be 100kΩ (10×10⁴), 105 would be 1MΩ (10×10⁵), and 205 is 2MΩ (20×10⁵). 751 is 750Ω (75×10¹), and 754 is 750kΩ (75×10⁴).

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.

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

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