resistor

Resistor Colour Codes

Bands
1 & 2 (& 3) 3 (or 4) 4 (or 5)
Colour Digit Multiplier Tolerance
Silver X 0.01 10%
Gold X 0.1 5%
Black 0 X 1
Brown 1 X 10 1%
Red 2 X 100 2%
Orange 3 X 1,000
Yellow 4 X 10,000
Green 5 X 100,000
Blue 6 X 1,000,000
Purple 7 X 10,000,000
Grey 8
White 9

What it all means....

Bands
The colour coding on resistors is arranged in Bands of colour around the body of the resistor (ceramic power resistors have the value printed directly on them).
They are read left to right, the left is identified by the colour band (NOT Silver or Gold) closest to the lead.

There may be either four or five bands, five bands indicate a higher tolerance resistor, IE: a tolerance level of 1 or 2%

Colour

a bit obvious I think

Digit

The number assigned to this colour, Not a value yet.

Multiplier

These colours show you how much to multiply the previous digits by to give you the value

Tolerance

Nothing is perfect in this world, so resistors are graded into tolerances, IE: Silver means the resistance shown is within +/- 10%, for example a 10 ohm resistor with the right most band being a Silver band is somewhere between 9 ohms and 11 ohms.

Example
brown red red silver
1 2 X 100 +/- 10%

= 1200 ohms OR 1.2k ohm with a tolerance of +/- 10%

Preferred Notation

This is the way you write down the value of a resistor, what you do is use the Metric Multiplier to replace the decimal point, the reason for this is a decimal point can easily be lost or obscurred in the above example 1.2k would become 1k2.
1,200,000 ohms or 1.2M would become 1M2.
0.22 ohms would become R22.
Note... if no metric Multiplier applies R indicates resistance, so 2.2 ohms becomes 2R2.

Preferred Values

Preferred values are what you can actually buy, it would be impossible to stock every possible value of resistance in a store or workshop, it is also unnecessary, as any resistance can be made up from combining multiple resistors, and in most cases it is not necessary to have the exact resistance your calculator tells you you need!.
The resistors are broken up according to the tolerance, the tolerance allows a slight overlap in resistances, Ie: a 10 ohm 10% resistor, has a possible value of 9-11 ohms. Therefore the next logical value would be 12 ohms which has a possible value of between @11ohms to @13ohms, and so on in this way all possible values within a range are covered

Table of preferred values
10%
10 12 15 18 22 27 33
47 56 68 82
5%
10 11 12 13 15 16 18
20 22 24 27 30 33 36
39 43 47 51 56 62 68
75 82 91
So if my calculator told me I needed a 6,095ohm resistor at a tolerance of 5%, I would look at the above table and select a (62)00 ohm resistor, this would have the following colours Blue(6) Red(2) Red(x 100) Gold(5%) which would hopefully look something like the resistor at the top of this page.


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