The attractive rainbow colors adorning most fixed resistors serve a purpose beyond catching your eye. Color-coding identifies the nominal value and tolerance of most resistors; the others are drab and boring, and have their values stamped on them.
The color code starts near the edge of one side of the resistor and consists of several stripes, or bands, of color. Each color represents a number, and the position of the band indicates how you use that number.
Standard-precision resistors use four color bands: The first three bands indicate the nominal value of the resistor, and the fourth indicates the tolerance. Using the following table, you can decipher the nominal value and tolerance of a standard-precision resistor as follows:
The first band gives you the first digit.
The second band gives you the second digit.
The third band gives you the multiplier as the number of zeros to tack on to the end of the first two digits — except if the band is gold or silver.
If the third band is gold, take the first two digits and divide by 10.
If the third band is silver, take the first two digits and divide by 100.
The fourth band tells you the tolerance, as shown in the fourth column. If there is no fourth band, you can assume the tolerance is +/–20%.
| Color | Band 1 (First Digit) | Band 2 (Second Digit) | Band 3 (Multiplier, or Number of Zeros) | Band 4 (Tolerance) |
|---|---|---|---|---|
| Black | 0 | 0 | 100 = 1 (no zeros) | +/–20% |
| Brown | 1 | 1 | 101 = 10 (1 zero) | +/–1% |
| Red | 2 | 2 | 102 = 100 (2 zeros) | +/–2% |
| Orange | 3 | 3 | 103 = 1,000 (3 zeros) | +/–3% |
| Yellow | 4 | 4 | 104 = 10,000 (4 zeros) | +/–4% |
| Green | 5 | 5 | 105 = 100,000 (5 zeros) | – |
| Blue | 6 | 6 | 106 = 1,000,000 (6 zeros) | – |
| Violet | 7 | 7 | 107 = 10,000,000 (7 zeros) | – |
| Gray | 8 | 8 | 108 = 100,000,000 (8 zeros) | – |
| White | 9 | 9 | 109 = 1,000,000,000 (9 zeros) | – |
| Gold | – | 0.1 (divide by 10) | +/–5% | |
| Silver | – | 0.01 (divide by 100) | +/–10% |
You get the nominal value of the resistance in ohms by putting the first two digits together (side by side) and applying the multiplier.
A resistor with five bands of color is a high-precision resistor. The first three bands of color give you the first three digits, the fourth band gives you the multiplier, and the fifth band represents the tolerance (typically +/–1%).
Colors vary greatly on resistor packaging, and some resistors don't use the color code at all, so you'd be wise to verify the actual resistance by using a multimeter set to ohms.