Circuit Innovations

Resistors are usually marked with either a 4 band or 5 band colour code. In the case of a 4 band code, the third band gives the multiplier and the fourth band gives the tolerance. In other words, ignore column 3 of the table above.

Just to add a bit more confusion, 5 band resistors actually have 6 bands and 4 band resistors actually have 5 bands. The last band refers to the temperature coefficient of the resistor and can generally be ignored unless you happen to be developing military or aerospace products.

How do I know which end to start reading from?

That's a good question as there is nothing on the resistor to tell you which end to start at. The answer only comes with experience as resistors are only made in certain values known as preferred values. This means that if you attempt to read the resistor backwards you will usually get a value that doesn't exist.

For example, a typical 5 band 1% tolerance resistor will have a red 6th band for the temperature coefficient. If you start reading at the wrong end, the first two digits will be red, brown or 21. Looking at the table of preferred values you will see that no resistor exists with 21 as its first digits.

As with all rules, you will probably find a few exceptions!