Question

Why do resistors have tolerance?

Answer 1

Resistors don't inherently have tolerance. They are made to certain tolerances. The common tolerances are: 1%, 2%, 5%, 10%, and 20%.

Certain circuits require precise voltage regulation or timing such as computers and audio equipment. So you need the resistors with tighter tolerances (lower percentage).

Why don't we just use 1% tolerance resistors? It has to do with cost. You need better materials and more quality checks to get the better tolerances.

What is tolerance? This is the amount that the resistance can varied from the specified value. So if you have a `1KOmega` resistor with 10% tolerance, the actual value of the resistor can be `900Omega` to `1100Omega`.

You should also be aware that temperature can raise/lower the resistance value.