How to read Resistor Colour Codes

How to read Resistor Colour Codes

First the code

 Black Brown Red Orange Yellow Green Blue Violet Gray White 0 1 2 3 4 5 6 7 8 9

NOTE:    5th band (Quality) not always used.

First find the tolerance band, it will typically be gold ( 5%) and sometimes silver (10%).

Starting from the other end, identify the first band - write down the number associated with that colour; in this case Blue is 6.

Now 'read' the next colour, here it is red so write down a '2' next to the six. (you should have '62' so far.)

Now read the third or 'multiplier' band and write down that number of zeros.

In this example it is two so we get '6200' or '6,200'. If the 'multiplier' band is Black (for zero) don't write any zeros down.

If the 'multiplier' band is Gold move the decimal point one to the left. If the 'multiplier' band is Silver  move the decimal point two places to the left. If the resistor has one more band past the tolerance band it is a quality band.

Read the number as the '% Failure rate per 1000 hour' This is rated assuming full wattage being applied to the resistors. (To get better failure rates, resistors are typically specified to have twice the needed wattage dissipation that the circuit produces). Some resistors use this band for temco information. 1% resistors have three bands to read digits to the left of the multiplier. They have a different temperature coefficient in order to provide the 1% tolerance.

At 1%  the temperature coefficient starts to become an important factor.  at +/-200 ppm a change in temperature of 25 Deg C causes a value change of up to 1%

BS 1852 Coding for resistor values

BS 1852(British Standard 1852). The letter R is used for Ohms and K for Kohms M for Megohms and placed where the decimal point would go.

At the end is a letter that represents tolerance Where M=20%, K=10%, J=5%, G=2%, and F=1% D=.5% C=.25 B=.1%

BS 1852 coding examples
R33 0.33 ohms
2R2 2.2 ohms
470R 470 Ohms
1K2 1.2K ohms
22K 22K ohms
22K2 22.2K ohms
4M7 4.7M ohms
5K6G 5.6K ohms 2%
33KK 33k Ohms 10%
47K3F 47.3 K Ohms 1%

Common surface mount coding

The third or forth digit is the multiplier

Thus 103 is a 10K resistor

475 is a 4.7M resistor