Reading Resistor Colour Codes

Resistors are a fundamental building block of most electronic circuits. Typical resistors used by hobbyists are in "through-hole" packages, with two leads and colour-coded stripes around the body to designate the value.



 In this example, the 4-band resistor has:
  • 1st band brown (1)
  • 2nd band black (0)
  • 3rd band orange (x 1000)
  • 4th band gold (5% tolerance)
The 4-band resistor therefore has a value of 10,000 Ohms: usually written as 10k. It also has a "tolerance" (accuracy) of +/-5%, so its actual value could be anywhere in the range 9,500 Ohms to 10,500 Ohms.

The 5-band resistor shown above has:
  • 1st band brown (1)
  • 2nd band black (0)
  • 3rd band black (0)
  • 4th band red (x 100)
  • 5th band brown (1% tolerance)
The 5-band resistor also has a value of 10k, but at a better +\-1% tolerance. That means its actual value could be anywhere in the range 9,900 Ohms to 10,100 Ohms. Both resistors therefore have the same nominal value, but the higher-accuracy resistor is likely to be closer to the actual value specified.

In most situations resistor values are not terribly important, so low-tolerance 5% resistors work just fine. In some specific situations higher-tolerance resistors are required, such as in calibration circuits for sensors or oscillators.