To manufacture resistors (or other components like capacitors) of every possible value would be impractical, instead they are made in a range of ‘Common Values’. The standard was created by Electronic Industries Association (EIA) and is often referred to as the “E” series. This series is broken into different tolerances:

E3 – 50% tolerance (no longer used)
E6 – 20% tolerance
E12 – 10% tolerance
E24 – 5% tolerance
E48 – 2% tolerance
E96 – 1% tolerance
E192 – 0.5, 0.25, 0.1% and higher tolerances

The number following the "E" specifies the number of logarithmic steps per decade and each step is the difference by tolerance (%). Below is the complete list of values for series E6 through to E192 (which are still being manufactured):