Explanation of Resistor Colour Code and Resistor Tolerances | Railwayscenics

Resistor colour bands

The coloured bands on a resistor can tell you everything you need to know about its value and tolerance, as long as you understand how to read them. The order in which the colours are arranged is very important, and each value of resistor has its own unique combination.

Graphical Resistor Calculator

This is a very simple four band graphical resistor calculator that will easily calculate the value of a resistor from the band colors.

Simply change the values from the dropdown menus to match the colour bands of your resoistor and the resistance value will automatically change.

Band 1Band 2Band 3Band 4
Value 1 (MSV)Value 2WeightTolerance
   

Resistance:  

1,000 Ω ±5%

Graphical Resistor Calculator Reference Chart

Standard Table For Calculating 4 Band Resistors' Resistance.

ColorDigit valueMultiplierMultiplied OutTolerance
Black01001
Brown110110
Red2102100
Orange31031,000
Yellow410410000
Green5105100,000
Blue61061,000,000
Violet710710,000,000
Gray8108100,000,000
White91091,000,000,000
Gold±5%
Silver±10%

Resistance values

The coloured bands on a resistor can tell you everything you need to know about its value and tolerance, as long as you understand how to read them. The order in which the colours are arranged is very important, and each value of resistor has its own unique combination.

4 Band resistor colours.

Here is an example that shows how the table and resistor shown above can be used to figure out a resistor value by proving that yellow-violet-brown is really 47k Ohm:

The first stripe is yellow, which means the leftmost digit is a 4.
The second stripe is violet, which means the next digit is a 7.
The third stripe is orange. Since orange is 1000, it means add three zeros to the right of the first two digits.
The fourth band is the tolerance band, which in this case is gold meaning 5%
Yellow - Violet - Orange = 4 - 7 - 000 = 47K Ohm.

Although the first two bands are fairly straightforward, the third (multiplier) and fourth (tolerance) bands might require a bit more explanation.

Multiplier band

Resistor values can get to be very high in number, and there often is not enough space to use a band for every digit. To get around this, the third band indicates that a certain number of zeros should be added after the first two digits to make up the full resistor value. In the example above, the third stripe is brown, indicating that a single zero should be added to the right of the first two digits.

If you want to go deeper into the maths, this third band is officially referred to as a multiplier. The colour of the band determines the power of 10 you need to multiply the first two resistor digits by.

Example:

Brown - black - orange resistor.
Brown = 1, black = 0, orange multiplier = 103
10 x 103 = 10000, which is the same as 10 + three zeros = 10000.

Notice that however you decide to think about it, the result ends up being the same.

Tolerance band

The fourth color band indicates the resistors tolerance. Tolerance is the percentage of error in the resistors resistance, or how much more or less you can expect a resistors actual measured resistance to be from its stated resistance. A gold tolerance band is 5% tolerance, silver is 10%, and no band at all would mean a 20% tolerance.

For Example:

A 220 Ohm resistor has a silver tolerance band.
Tolerance = value of resistor x value of tolerance band = 220 Ohm x 10% = 22 Ohm
220 Ohm stated resistance +/- 22 Ohm tolerance means that the resistor could range in actual value from as much as 242 Ohm to as little as 198 Ohm.

Some projects require your measurements to be more precise than others, and for this reason the tolerance band is useful in identifying which resistor will give you a more accurate resistance reading. The smaller the tolerance percentage is, the higher the precision in your measurements.