Resistor Tolerance

The tolerance of a resistor is the deviation (in percentage) of the resistor, in percentage, from its nominal value resistance, measured at 25°C with no load applied.

Typical resistor tolerances are 1 percent, 2 percent, 5 percent, 10 percent and 20 percent. The value can even be lower than 1 percent with high-precision resistors.

Just to see some practical examples of what tolerance is, consider a 500Ω resistor with a 10 percent tolerance. This means that the resistance of it can be anywhere from as low as 490Ω to as high as 510Ω. On the other hand, if the same 500Ω resistor has a 1 percent tolerance, its resistance can be between 499Ω and 501Ω. Lower percent tolerances equal more precision (less variance) in resistance values.

Carbon-composition resistors, as a whole, have the worst tolerance levels, around 5 to 20 percent. Carbon-film resistors are about 1 to 5 percent, metal-film about 1 percent, and precision metal-film resistors as low as 0.1 percent. Most wirewound resistors are from 1 to 5 percent, while precision wirewounds can achieve ±0.005 percent tolerances. Foil resistors can achieve 0.0005 percent.

For most general applications, a resistor with a 5 percent tolerance is adequate.