By Kim Lewis Updated Mar 24, 2022
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Electrical resistors are marked with color bands that denote their resistance value and other specifications. The fourth band specifies the tolerance, expressing how closely the resistor’s actual resistance matches its nominal value. Tolerance is expressed as a percentage difference between the measured resistance and the ideal value.
Resistors that display only three color bands omit the tolerance band, which defaults to ±20%. For example, a 1 kΩ resistor can actually range from 800 Ω to 1,200 Ω.
Silver indicates ±10% tolerance; gold indicates ±5%. Resistors with tolerances of 1% or lower—marked with colors such as brown or green—are used where high precision is required.
Refer to a resistor color‑code chart to decode the tolerance band. Measuring a resistor with a digital multimeter lets you compare its real resistance to the nominal value.
Most hobbyist, educational, and consumer circuits use standard resistors with ±20% tolerance. In contrast, mission‑critical applications—e.g., spacecraft electronics—require precision resistors with tolerances of 1% or less.
