The Resistor Color Code

## The Resistor Color Code

Most resistors are labeled using colored bands painted on the resistor. You should be able to read the color code as well as calculate whether a resistor is within tolerance. Here is the color code and how to decipher it.

 The Resistor Color Code 0 = Black 5 = Green 1 = Brown 6 = Blue 2 = Red 7 =  Purple 3 = Orange 8 = Grey 4 = Yellow 9 = White

One acronym used to help remember the color code is Better Be Ready Or Your Great Big Plan Goes Wrong, as shown below.

 Better Be Ready Or Your Great Big Plan Goes Wrong Black Brown Red Orange Yellow Green Blue Purple Grey White 0 1 2 3 4 5 6 7 8 9

The following diagram shows how the colors are used. The first two bands are values of resistance and the third band is a multiplier.
 The Colors on a Resistor

Essentially a resistor is read as: first number, second number, number of zeros. For example, if the colors are yellow-purple-red, the numbers are 4-7-2. This reads 4, 7 and two zeros or 4,700 ohms. If the colors are brown-black-orange, the numbers are 1-0-3. This reads 1, 0 and three more zeros or 10,000 ohms. If the colors are green-red-black, the numbers are 5-2-0. This reads 5, 2 and no zeros or 52 ohms. If the third band is gold or silver, the resistor has a value of less than 10 ohms. Gold denotes a multiplier of 0.1 and silver denotes a multiplier of 0.01. For example, if the colors are brown-black-gold, the numbers are 1-0-1/10. This reads 1, 0, then divide by 10 for 1 ohm. Brown-black-silver would be 0.1 ohm. A single black band is 0 ohms. This is merely a shorting wire or jumper that looks like a resistor.

Exercise: decode the following colors1

 red-black-orange = __________ ohms orange-red-brown = __________ ohms brown-red-red = __________ ohms purple-green-black = __________ ohms blue-white-yellow = __________ ohms yellow-purple-gold = __________ ohms

Precision resistors have four colors bands instead of three (excluding the tolerance band). These resistors are read: first number, second number, third number, number of zeros. For example, a 10,000-ohm resistor would normally be marked brown-black-orange. A precision 10,000-ohm resistor would be marked brown-black-black-red.

Exercise: decode the following colors for precision resistors1

 red-black-black-red = __________ ohms orange-red-black-black = __________ ohms brown-red-black-black = __________ ohms purple-green-black-gold = __________ ohms blue-white-black-orange = __________ ohms yellow-purple-black-silver = __________ ohms

### Calculating tolerance

The tolerance band will be either silver or gold. Silver is 10% tolerance and gold is 5% tolerance. If there is no fourth band, the tolerance is 20%.

To calculate resistor tolerance limits, follow this procedure:
• Multiply the specified resistance by the tolerance.
• Add this product to the specified resistance. This gives you the highest allowed value.
• Subtract the product from the specified resistance. This gives you the lowest allowed value.
For example, if you have a resistor that is colored Yellow-Purple-Orange-Gold, the resistor is 47,000 ohms with a 5% tolerance. Calculate the allowed range of resistance like this:

 1 47,000 X .05 = 2,350 2 47,000 + 2,350 = 49,350 – this is the highest allowed value 3 47,000 - 2,350 = 44,650 – this is the lowest allowed value

This 47,000-ohm resistor may have a resistance that ranges from 44,650 ohms to 49,350 ohms and still be within the specified tolerance.

Exercise: which of the following values is within the tolerance of an Orange-Orange-Orange-Gold resistor?2

a. 34,720  b. 32,770  c. 34,670  d. 31,330

A resistor with four color bands (where the fourth band is neither silver nor gold) has a tolerance of 1%. A 1% resistor may also have a fifth band that is brown. The following table shows the tolerance colors (fifth band) for precision resistors.

 Tolerance Codes for Precision Resistors 1% = Brown or none .25% = Blue 2% = Red .1% = Purple .5% = Green .05% = Grey

### Power rating

Power will be discussed below after Ohm's Law. However, since power is produced when current flows through a resistor, resistors are rated for how much power they can dissipate safely. Since power produced in resistors is manifested as heat, and larger resistors can dissipate more heat than smaller resistors, the size of a resistor is a direct product of its power capacity.

There is no set size scale for rating power capacity of resistors, but typical resistors (about 3/32 inch diameter and 5/16 inch long) have a power capacity of 1/4 watt. A 1/2 watt resistor is notably larger and a 1/8 watt resistor is notably smaller. High-power resistors may have metal cases with heat dissipating fins and be designed to be mounted on heat sinks.

 1 20,000 (20k)    |           320          1,200 (1.2k)   |             75                           690,000 (690 k) |            4.7 The precision resistors are the same answers 2 b. 32,770 ohms

The Resistor Color Code