Resistors

Resistor Color Code Calculator

This resisitor calculator requires the use of Javascript enabled and capable browsers. For operational and other information, and for those unable to use the calculator because of browser limitations, there is a resistor color code chart below the calculator and additional information below the table. For those in the electronics business that are color blind (as I am), working with resistorsand color coded capacitors can be difficult. This table names (as well as shows) the colors and the values. To use the calculator, select a value from the vertical group of Color Band 1, from Color Band 2 and from Color Band 3. Immediately to the left of the Calculate Values button below the three bands, there are three boxes that upon selection of a color from the bands, an identifying number and color will correspond in appearance. After selecting a value from all three bands, click on Calculate Values and the resistor's value is calculated and will appear as well as a text representation of the three bands. This calculator does not consider the 4th Band, tolerance, since it would not change the calculation. You may change a value by again clicking on the band values from any of the three bands but be sure to click on Calculate Values after each selection to update the correct information of resistor value and color band text representation.

Color Band 1 Color Band 2 Color Band 3  OR

Resistor Color Code Chart

Band Color Options Band #1 Possible Band #2 Possible Band #3 Possible Multiplier Value For Band 3 Band #4 Value Tolerance Black 0 1 1 Brown 1 1 1 10 Red 2 2 2 100 Orange 3 3 3 1,000 Yellow 4 4 4 10,000 Green 5 5 5 100,000 Blue 6 6 6 1,000,000 Violet 7 7 10,000,000 Gray 8 8 100,000,000 White 9 9 1,000,000,000 None 20% Silver 10% Gold 5%

Resistor Color Code Information

The resistor color code is a long standing standard in both the electronics and electrical industries, indicating the value of resistance of a resistor. Resistance is measured in ohms and there is a foundation for it called Ohm's Law. (Want to know about Ohm's Law? If so, please click here or click here!) Each color band represents a number and the order of the color band will represent a number value. The first 2 color bands indicate a number. The 3rd color band indicates the multiplier or in other words the number of zeros. The fourth band indicates the tolerance of the resistor +/- 20%, 10% or 5%. In most cases, there are 4 color bands. However, certain precision resistors have 5 bands or have the values written on them, refining the tolerance value even more. There is no standard (TANS) however, for the 5th band. From one manufacturing company to another, the 5th band may indicate 2%, 1%, 1/2% or even closer, according to their own standards. Color bands are usually found on resistors that have a wattage value of 1/8 to 2 watts; though it is rare, there are some 5 watt resistors that are banded. There are also some capacitors that are color coded. See our Capacitor Color Code Calculator.

Resistors

Colour Code | Tolerance | Real Values (E6 & E12 series) | Power RatingAlso see: Resistance | Ohm's Law
Example:       Circuit symbol:   

Function

Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when soldering.

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The Resistor Colour Code
Colour	Number
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet	7
Grey	8
White	9

Resistor values - the resistor colour code

Resistance is measured in ohms, the symbol for ohm is an omega .
1  is quite small so resistor values are often given in k and M.
1 k = 1000      1 M = 1000000 .Resistor values are normally shown using coloured bands.
Each colour represents a number as shown in the table.
Most resistors have 4 bands:

• The first band gives the first digit.
• The second band gives the second digit.
• The third band indicates the number of zeros.
• The fourth band is used to shows the tolerance (precision) of the resistor, this may be ignored for almost all circuits but further details are given below.

This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000  = 270 k.
On circuit diagrams the  is usually omitted and the value is written 270K.
Find out how to make your own Resistor Colour Code Calculator

Small value resistors (less than 10 ohm)

The standard colour code cannot show values of less than 10. To show these small values two special colours are used for the third band:gold which means × 0.1 and silver which means × 0.01. The first and second bands represent the digits as normal.For example:
red, violet, gold bands represent 27 × 0.1 = 2.7 
green, blue, silver bands represent 56 × 0.01 = 0.56 

Tolerance of resistors (fourth band of colour code)

The tolerance of a resistor is shown by the fourth band of the colour code. Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between 390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390).A special colour code is used for the fourth band tolerance:
silver ±10%,   gold ±5%,   red ±2%,   brown ±1%.
If no fourth band is shown the tolerance is ±20%.
Tolerance may be ignored for almost all circuits because precise resistor values are rarely required.

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Resistor shorthand

Resistor values are often written on circuit diagrams using a code system which avoids using a decimal point because it is easy to miss the small dot. Instead the letters R, K and M are used in place of the decimal point. To read the code: replace the letter with a decimal point, then multiply the value by 1000 if the letter was K, or 1000000 if the letter was M. The letter R means multiply by 1.For example:

560R means 560  2K7  means 2.7 k = 2700  39K  means 39 k 1M0  means 1.0 M = 1000 k

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Real resistor values (the E6 and E12 series)

You may have noticed that resistors are not available with every possible value, for example 22k and 47k are readily available, but 25k and 50k are not!Why is this? Imagine that you decided to make resistors every 10 giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits. In fact it would be difficult to make resistors sufficiently accurate.
To produce a sensible range of resistor values you need to increase the size of the 'step' as the value increases. The standard resistor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.
The E6 series (6 values for each multiple of ten, for resistors with 20% tolerance)
10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc.
Notice how the step size increases as the value increases. For this series the step (to the next value) is roughly half the value.
The E12 series (12 values for each multiple of ten, for resistors with 10% tolerance)
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, ... then it continues 100, 120, 150 etc.
Notice how this is the E6 series with an extra value in the gaps.
The E12 series is the one most frequently used for resistors. It allows you to choose a value within 10% of the precise value you need. This is sufficiently accurate for almost all projects and it is sensible because most resistors are only accurate to ±10% (called their 'tolerance'). For example a resistor marked 390 could vary by ±10% × 390 = ±39, so it could be any value between 351 and 429.

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Resistors in Series and Parallel

For information on resistors connected in series and parallel please see the Resistance page,

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Power Ratings of Resistors

High power resistors (5W top, 25W bottom)

Electrical energy is converted to heat when current flows through a resistor. Usually the effect is negligible, but if the resistance is low (or the voltage across the resistor high) a large current may pass making the resistor become noticeably warm. The resistor must be able to withstand the heating effect and resistors have power ratings to show this.Power ratings of resistors are rarely quoted in parts lists because for most circuits the standard power ratings of 0.25W or 0.5W are suitable. For the rare cases where a higher power is required it should be clearly specified in the parts list, these will be circuits using low value resistors (less than about 300) or high voltages (more than 15V).
The power, P, developed in a resistor is given by:

P = I² × R or P = V² / R

where:

P = power developed in the resistor in watts (W) I  = current through the resistor in amps (A) R = resistance of the resistor in ohms () V = voltage across the resistor in volts (V)

Examples:

• A 470 resistor with 10V across it, needs a power rating P = V²/R = 10²/470 = 0.21W.
  In this case a standard 0.25W resistor would be suitable.
• A 27 resistor with 10V across it, needs a power rating P = V²/R = 10²/27 = 3.7W.
  A high power resistor with a rating of 5W would be suitable.