Most through-hole resistors are marked with color bands to indicate their value and tolerance (and occasionally other things like temperature coefficients). Here is a summary of the color code for 4 and 5 band resistors. Resistors with a tolerance of 5% or greater usually only have 4 bands because they only have 2 significant digits in their values. 2% and 1% resistors have 3 significant digits and thus need an additional band to represent their value.

Color | Band 1 | Band 2 | (not present) | Band 3 | Band 4 | 4 Bands |
---|---|---|---|---|---|---|

Band 3 | Band 4 | Band 5 | 5 Bands | |||

Black | 0 | x1 | ||||

Brown | 1 | x10 | 1% | |||

Red | 2 | x100 | 2% | |||

Orange | 3 | x1,000 (x 1k) |
||||

Yellow | 4 | x10,000 (x 10k) |
||||

Green | 5 | x100,000 (x 100k) |
0.5% | |||

Blue | 6 | x1,000,000 (x 1M) |
0.25% | |||

Violet | 7 | x10,000,000 (x 10M) |
0.1% | |||

Gray | 8 | x100,000,000 (x 100M) |
0.05% | |||

White | 9 | x1,000,000,000 (x 1G) |
||||

Gold | x0.1 | 5% | ||||

Silver | x0.01 | 10% |

If you find a resistor with only 3 color bands, it is most likely a 20% tolerance resistor, which is rarely used today and can probably be substituted with a 10% or 5% tolerance resistor. The 3 bands represent the value and multiplier. Thus a resistor marked yellow-violet-brown-gold would be a 470Ω 5% tolerance resistor.

In some situations colors can be difficult to distinguish, but for 4 band resistors, we can usually identify the correct value by checking against the 24 standard values. For example if we saw a resistor that looked like it was yellow-blue-brown (which would be 460Ω), we could assume it was more likely yellow-violet-brown, since 470Ω is a standard value. The other possibility would be orange-blue-brown, or 360Ω.

Standard values for 5% tolerance (E24 series) resistors are the following base values times power of 10:

10 | 11 | 12 | 13 |

15 | 16 | 18 | 20 |

22 | 24 | 27 | 30 |

33 | 36 | 39 | 43 |

47 | 51 | 56 | 62 |

68 | 75 | 82 | 91 |

On surface mount and some specialty resistors, the resistor value is marked as 3 or 4 digits and possibly a letter indicating tolerance. The first 2 or 3 digits represent the value, where the last digit represents the multiplier: essentially the number of zeros after the value digits. Thus, a resistor marked 471 would be a 470Ω resistor. Common tolerance codes are J for 5%, G for 2%, and F for 1%. If tolerance is not marked, the tolerance must be found in the manufacturer’s datasheet, but it can be narrowed down by significant digits. A 4 digit marking has 3 significant digits and is normally only used on 2% or better resistors. If a resistor only has a 3 digit marking, it is most likely 5% (or possibly 10%) tolerance.