In electronics, resistors are used when building circuits to reduce current flow by increasing resistance. Resistors have several uses: They adjust signal levels, divide voltages, and terminate transmission lines, to name a few.
Resistance is shown by the symbol R and is measured in Ohm (Ω). Resistors can have resistance values from mere fractions of a single Ohm to millions of ohms, depending on their use.
Knowing which resistor to use in specific contexts is important, and involves an understanding of the color coding used to classify resistors, according to their tolerance and multiplier levels. These define the magnitude of a resistor, which in turn determines the resistor’s specific function.
Understanding these color codes is important, and this calculator will enable you to interpret these codes and calculate the magnitude of resistance from the color coding.
It is useful to define the relationship between voltage, current, and resistance in trying to understand how to read color codes and use resistors.
Ohm’s Law is what describes this connection. It states that the current flowing through a conductor is proportional to the voltage between the ends of the conductor. This is shown below, where the constant of proportionality is the resistance.
I is the current (amperes), and V is the voltage across the conductor (measured in volts). R, resistance, is measured in Ohms.
Color coding of resistor bands
Resistor color coding provides an internationally accepted system for measuring and classifying resistors.
The international standard, IEC 60062. In the 1950s, the International Electrotechnical Commission decided to create this norm as resistors were being manufactured at an increasing level.
The color codes are linked to a numerical coding impossible to record on very small resistors. The color code is given by several bands and is it the ordering and distancing of these bands that informs the interpretation of the code. A resistor can have three to six bands.
One of these bands always represents a multiplier value, and one of the bands always represents the tolerance, which is a measure of deviation from the preferred or expected level of resistance. This works as an error term and provides space for a deviation around the predicted value.
Thus, the color coding on a resistor begins with a set of what are called ‘significant values.’ The last band represents the tolerance, and the second-to-last band represents the multiplier.
The resistance, measured in Ohms of the resistor, is shown by taking ordering the integers indicated by the ‘significant value’ bands, times the multiplier, a band which is included to rapidly increase the magnitude, as there is no space for the number of bands required for large numbers! The multiplier band is color-coded to show which power of ten should be used in calculating the overall resistance.
Reading the Resistors Color Code
The left-hand band is the first digit. This is considered the most significant band, and this will be nearest to a connecting lead. Read from left to right then, we get
Digit, Digit, Multiplier
This is then indicated by the first color, the second color, and 10color, and the figure is measured in Ohms.
Green, Blue, Red, with a gold line at the furthest end can be interpreted as follows:
56 x 102 = 5600 Ω
How to use this calculator
This calculator allows you to set the number of bands, and then to enter the colors for each of the bands. This will provide a figure for the resistance of the resistor.
You will need to know which side to start reading from. The tolerance band, the last band on the resistor will usually be set further from the other bands, and this band may be gold or silver in color.
Position the tolerance band on the right, and read the colors from left to right. Enter the colors into the calculator and it will present the result.
Whether you are building electronic components or large electrical circuits, it is good to know this information on resistance.