Foundation Radio Amateur Licence - BDARS Online Syllabus

Resistor Calculator

Resistors are color coded for easy reading !!.

To determine the value of a given resistor look for the gold or silver tolorance band and rotate the resistor as in the picture the the left.(Tolerance band to the right).
Look at the 1st color band and determine its color.
Now look at the chart and match the "1st colour band" colour to the "Digit it represents". Write this number down.

Now look at the 2nd color band and match that color to the same chart. Write this number next to the 1st Digit.

The Last color band is the number you will multiply the result by. Match the 3rd color band with the chart under multiplier. This is the number you will mulitple the other 2 numbers by. Write it next to the other 2 numbers with a multiplication sign before it. Example : 2 2 x 1,000.

To pull it all together now, simply multiply the first 2 numbers (1st number in the tens column and 2nd in the ones column) by the Multiplier. so the resistor in the example is coded Red, Violet, Orange, Gold - 2 7 x1000 = 27000 or 27k for short, the last band is Gold so the value is +/- 5% Tolerance...


Tolerance Explanation

Resistors are never the exact value that the color codes indicate. Therefore manufacturers place a tolerance colour band on the resistor to tell you just how accurate this resistor is made. It is simply a measurment of the imperfections. Gold means the resistor is within 5% of being dead-on accurate. Silver being within 10% and no color band being within 20%. To determine the exact range that the resistor may be, take the value of the resistor and mutiply it by 5,10, 0r 20%. That is the number that the resistor may go either way.

Example: A 1,000 Ohm resistor with a gold band maybe any value between 950 to 1050 Ohms.

Example: A 22,000 Ohm resistor with a silver band maybe any value between 19,800 and 24,200 Ohms.

Now you are ready to use this Resistor Calculator below, just for fun see if you can work out the value of a resistor coded Brown, Black, Orange, Silver, once you have your answer check it here..