This guide is relevent to all resistors, it is written to support the sales of all sizes of E12 resistors, 1/4 watt from my shop mallinson-electrical.
Most Resistors used in electronics will be colour coded to give their value.
This is a brief explanation of how to read the codes on the most commonly used resistors, namely the values in the E12 series
it is a simple matter of reading from left to right and assigning a value to the coloured bands.
The final band (band 4) indicates the tolerance of the resistor
To determine which way round to read the resistor is easy enough, if you read the number correctly it will be one of the standard sizes available
The E12 series all start with one of these values;
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 or 82
there are, as you can see "12" values, hence E12. No matter which resistor you pick up it will be one of these values, multiplied by a factor of 10.
code Brown, Black, Green, Gold
reading this way round gives 1,0, x100,000, 5% = 1,000,000 with 5% tolerance i.e. 1 Mohm
It cannot be the other way round, as no resistor starts with Gold
code Brown, Red, Brown, Red
read this way = 1,2,x10, 2%tolerance =120 ohms ok
read in reverse= 2, 1, x100, 1% = 2100 ohms. There is no value in E12 starting 2,1, so it must be the first way we tried.
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All Resistor Listings have a colour code chart on the page