How To Calculate And Understand Resistor Values

Resistor Color Code Bands
& Other Component Identification

Resistor Color Code Identification

Resistor Color Codes
While these codes are most often associated with resistors, then can also apply to capacitors and other components.
The standard color coding method for resistors uses a different color to represent each number 0 to 9: black, brown, red, orange, yellow, green, blue, purple, gray, white. On a 4 band resistor, the first two bands represent the significant digits. On a 5 and 6 band, the first three bands are the significant digits. The next band represents the multiplier or "decade". As in the above 4 band example, the first two bands are red and purple, representing 2 and 7. The third band is orange, representing 3 meaning 103 or 1000. This gives a value of 27 * 1000, or 27000 Ohms. The gold and silver decade bands divide by a power of 10, allowing for values below 10 Ohms. The 5 and 6 band resistors work exactly the same as the 4 band resistor. They just add one more significant digit. The band after the decade is the tolerance. This tells how accurate the resistance compared to its specification. The 4 band resistor has a gold tolerance, or 5%, meaning that the true value of the resistor could be 5% more or less than 27000 Ohms, allowing values between 25650 to 28350 Ohms. The last band on a 6 band resistor is the temperature coefficient of the resistor, measured in PPM/C or parts per million per degree Centigrade. Brown (100 PPM/C) are the most popular, and will work for most reasonable temperature conditions. The others are specially designed for temperature critical applications.

Alpha-Numeric Code Identification

Alpha Numeric Codes
With the sizes of resistors and other components shrinking or changing in shape, it is getting difficult to fit all of the color bands on a resistor. Therefore, a simpler alphanumeric coding system is used. This method uses three numbers, sometimes followed by a single letter. The numbers represent the same as the first three bands on a 4 band resistor. On the above SIL network, the 4 and 7 are the significant digits and the 3 is the decade, giving 47 x 1000 or 47000 Ohms. The letter after the numbers is the tolerance. The different representations are: M=±20%, K=±10%, J=±5%, G=±2%, F=±1%.

This calculator solves for 4, 5 or 6 band resistors and is quite simple to use. To calculate a four band resistor value, use the middle four"drop" boxes then click on the "Calc 4 Band" button. For a five or six band resistor, you can use all six boxes but all 6 do not necessarily have to be used - the "Temperature Coefficient" box, for example. After you have selected the 6 "drop box" choices, remember to click the "Calc 5 Band" button for your answer.
If you have calculated a 5 or 6 band resistor, and go back to calculating a 4 band resistor, the two drop boxes on the ends (far left and far right) will not clear but this is perfectly all right. When calculating 4 band resistors, the values of the drop boxes on the ends do not enter into the calculations in any manner.

Four   Band   Resistors  
Resistors are electronic components that oppose the flow of electricity and the resistance is measured in ohms. For larger values,kilohms (1,000 ohms) and megohms (1,000,000 ohms) are used. For example 3,300 ohms equals 3.3 kilohms or just 3.3 k and 1,500,000 ohms equals 1.5 megohms or 1.5 meg.Color "bands" are used to indicate the resistance value with each color signifying a number and these color bands are grouped closer to one end of the resistor than the other.
As can be seen in the above 4 Band Resistor Color Codes chart, the first two color bands have values of brown = 1, red = 2, orange = 3 and so on.The third color band is the multiplier of the first 2 bands. Here, black is 1, brown is 10, red is 100 and so on. Putting this in other words, the value of the third band (the multiplier) is the number 10 raised to the power of the color code. For example, red in the third band is 10² or 100.
This third band also has 2 new colors where gold = .1 and silver = .01.
The 4th band is the resistor's tolerance and shows how precisely the resistor was manufactured. Gold = 5%, silver = 10% and no band whatsoever = 20%.
Now that we know the values of each color, let's try calculating a few examples of resistance values.
Looking at resistor #1, we see the colors red red green gold.
The Color Codes chart "translates" this into 2 2 and 100,000
which equals 2 2 ×100,000 or 2,200,000 ohms and don't forget the gold 4th band which indicates a 5% tolerance.
Resistor #2 has the colors orange orange yellow silver which "translates" into 3 3 ×10,000 or 330,000 ohms and a tolerance of 10%.
Resistor #3 has the colors yellow violet silver meaning 4 7 ×.01 or .47 ohms and no fourth band indicates a 20% tolerance.

Five Band Resistors

Use the 5 Band Chart to solve these next problems.
For resistor 4, we see the first 3 bands are violet, green and red which "translate" into 7, 5 and 2. Looking at the fourth band (the multiplier), we see it is brown and has a value of 10.
So, the resistance value is 7 5 2 × 10 which equals 7,520 ohms or 7.52 K ohms.
Band 5 is red which indicates a 2 per cent tolerance and a brown sixth band means that the temperature coefficient is 100 parts per million (ppm).Examining resistor 5, the first 3 bands are brown, black and blue and the fourth band (the multiplier) is green. So, these colors convert into 1 0 6 × 100,000 which calculates to 10,600,000 ohms or 10.6 Meg ohms.
The brown 5th band and the red 6th band mean that the resistor has a 1% tolerance and a 50 ppm temperature coefficient.

If you've read these instructions, you probably have a good understanding of determining a resistor's value from its colors. Then again, there's always the calculator which makes things much easier to solve.


resistor is a device that opposes the flow of electrical current. The bigger the value of a resistor the more it opposes the current flow. The value of a resistor is given in ohms and is often referred to as its ‘resistance’.

Identifying Resistor Values

Band Colour1st Band2nd BandMultiplier xTolerance
Silver÷ 10010%
Gold÷ 105%

Example: Band 1 = Red, Band 2 = Violet, Band 3 = Orange, Band 4 = GoldToo many zeros?
The value of this resistor would be:kilo ohms and mega
2 (Red) 7 (Violet) x1,000 (Orange)= 27 x 1,000ohms can be used:
= 27,000 with a 5% tolerance (gold)1,000 ohms =1k
= 27k ohms1,000k = 1M

Resistor Identification Task

Calculate the resistor values given by the bands shown below. The tolerance band has been ignored.
1st Band2nd BandMultiplier xValue

Calculating Resistor Markings

Calculate what the colour bands would be for the following resistor values.
Value1st Band2nd BandMultiplier x
180 ohms
3,900 ohms
47,000 ohms (47k)
1,000,000 ohms(1M)

What does Tolerance mean?

Resistors always have a tolerance but what does this mean? It refers to the accuracy to which it has been manufactured. For example if you were to measure the resistance of a gold tolerance resistor you can guarantee that the value measured will be within 5% of its stated value. Tolerances are important if the accuracy of a resistors value is critical to a designs performance.

Preferred Values

There are a number of different ranges of values for resistors. Two of the most popular are the E12 and E24. They take into account the manufacturing tolerance and are chosen such that there is a minimum overlap between the upper possible value of the first value in the series and the lowest possible value of the next. Hence there are fewer values in the 10% tolerance range.

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