Resistor Color Code Calculator

Decode a 4-band resistor's color code into its resistance value and tolerance

Decoding a resistor's color bands into its actual resistance value and tolerance requires correctly reading each band's position and meaning — the color-to-number mapping is a fixed industry standard, but misreading which band is which (especially confusing the first significant-figure band with the tolerance band) produces a completely wrong resistance reading.

Why band position and order matter as much as the colors themselves

A standard 4-band resistor uses the first two bands to represent significant figures, the third band as a multiplier (how many zeros to add, or a decimal-place adjustment), and the fourth band specifically to indicate tolerance (how much the actual resistance may vary from the nominal marked value) — each color maps to a specific digit or multiplier value under a fixed, universal color-code standard, but that mapping only produces a correct reading if the bands are read in the correct order and direction. Reading the bands backward (right to left instead of left to right, which is a genuinely easy mistake on a small physical component) produces a different, incorrect resistance value, since the significant-figure and multiplier bands play different roles depending on their position.

A worked example

The same set of colored bands read in the correct order versus the reversed order produces two different calculated resistance values — resistor color bands aren't symmetric or order-independent, so correctly identifying which end of the resistor to start reading from (typically indicated by the tolerance band being spaced slightly apart from the others) is a necessary first step before the color-to-number mapping can be applied correctly.

How this connects to your other technical calculations

Once a resistor's actual resistance value is correctly decoded, that figure becomes a direct input to the Ohm's Law Calculator for calculating voltage, current, or power in a circuit containing that specific resistor — accurate color-code decoding is the necessary first step before any downstream circuit calculation involving that component.

Common mistakes

Reading the color bands starting from the wrong end of the resistor (which reverses the significant-figure and multiplier roles) is the most common decoding error — always identify the tolerance band first (typically gold or silver, and spaced slightly apart from the other bands) to correctly establish reading direction before decoding the remaining bands.