Resistor Value and Ratio Calculator

Resistor Value and Ratio Calculator

Sometimes we need a resistor value more precice than what is offered in the standard series. For this task, use the Resistor Value Calculator.

A more complicated task is to pick resistors to satisfy a ratio. This is often done to set the division ratio in a voltage divider, for example. This is where the Resistor Ratio Calculator comes in handy.

Resistor Series

There are four more or less commonly used resistor series, with 12, 24, 48, and 96 values per decade, respectively. Generally, 5% tolerance resistors are available in E24 and 1% resistors in E96, but this is not a hard and fast rule. For example some low-value 1% resistors are available in E12 only.

E12       (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82)
E24       (10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, ..., 82, 91)
E48       (10.0, 10.5, 11.0, 11.5, 12.1, 12.7, 13.3, ..., 90.9, 95.3) 
E96       (10.0, 10.2, 10.5, 10.7, 11.0, 11.3, 11.5, ..., 95.3, 97.6) All values

Resistor Value

Find the best single resistor, series, and parallel resistor combination from the series selected above to satisfy the desired value.

Desired value: Ω  KΩ  

Single:
Series: + =
Parallel: // =

Resistor Ratio

Find the best combination of resistors to satisfy the given ratio, using values from the series selected above.

Select which type of ratio to solve for:

Resistor ratio       R1/R2
Voltage divider     R1 / (R1+R2)   valid range: 0.0 < ratio < 1.0
Desired ratio: Inverse What is this?


Single: ÷ =
Series: ÷ ( + ) =
Parallel: ÷ ( // ) =
How does it work?

The results are guaranteed to be the best choices within a decade of values. You can scale all the resistor values up or down by factors of 10 without changing the accuracy.