Resistor color codes

Standard through-hole resistors use a common color code to easily identify its specifications. The code is a series of four or five bands, though the four band code is the most common. Resistor values are always coded in ohms (Ω).

In the typical four band code, there is a gap between the third and fourth band, which indicates the left and right sides.

Reading from left to right: Band 1 is the first significant figure Band 2 is the second significant figure Band 3 is the decimal multiplier Band 4 indicates the tolerance value, in percent (no color indicates 20%)

Using the example above, red, violet, green, and gold will have the the first digit 2, second digit 7, multiplied by 10^5: 2,700,000 Ohms (2.7M Ohms). The gold band shows that the tolerance is +/- 5%, so the true resistance could lie between 2,565,000 and 2,835,000 Ohms.

Resistors created for military use can also include a fifth band, indicating the failure rate or reliability. Tight tolerance resistors, too, may have three bands for significant figures instead of two, where Bands 1-3 indicate significant figures, Band 4 is the multiplier, and Band 5 is the tolerance. Alternatively, it may have two significant figures, and the fifth band would represent the temperature coefficient in units of ppm/K.

All color coded resistors will have at least two value bands, and a multiplier. The remaining bands are optional.

The standard code per EN 60062:2005 is:

The colors used for the figures and tolerances also follow the visible light spectrum: red, orange, yellow, green, blue, violet. Black has no energy (0), and brown has "a little more" (1). White has "everything" (9), and grey is like white but less intense (8).

Resistors are also produced using preferred numbers, where each decade of values is divided into a series of value steps. These steps ensure that arbitrary values are replaced with the nearest preferred number, which keeps the maxiumum relative error within a specific range. The values repeat in every decade of magnitude (6.8, 68, 680, etc.)

There are also Zero ohm resistors, which are a length of wire wrapped in a resistor-shaped body. These can be substituted for another value in automatic insertion equipment. They are marked by a single black band.

Mnemonics
There are several useful mnemonics for memorizing the color code. Tolerance codes are typically not included.
 * Bad boys ravish our young girls but Violet gives willingly.
 * Bad beer rots our young guts but Vodka goes well.