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 |