As you probably know, the Electronic Industries Association (EIA) and other authorities have specified standard values for resistors. It can be referred as the Preferred Value system.
The preferred value system has its origins in the early years of the last century at a time when most resistors were carbon-graphite with relatively poor manufacturing tolerances.
The E series specify the preferred values for various tolerances. The number following the E specifies the number of logarithmic steps per decade.
This is not really a calculator, but a very handy tool if, like me, you can't remember what values of resistor are available "from stock".
Enter the value of resistor you would like in the box and the available values from the different series and the difference (as a percentage) from the required value is displayed below. This is a rolling calculation and does not require clearing, just alter the value in the box.