Standard resistor values
The resistance of resistors often follows the E series. The E series consists of the E3, E6, E12, E24, E48, E96 and E192 series. A higher number correlates to a lower tolerance and a higher precision. All standard resistor values can be found in the table below.
Bob needs a 250 ohm resistance and wants to use an E24 series resistor. What resistor should he use?
First, we convert the resistance to a number between 0 and 10. 250 becomes 2.5 in this case. The table shows 2.4 and 2.7 in the column for E24. It is better to round up even though 2.4 is closer to 2.5 than 2.7 to prevent overvoltage. Bob should use a 270 ohm resistor.