# Calculate R and C for impedance

Calculator and formulas for calculating R and C for a given impedance and cutoff frequency

## Calculate resistor and capacitor

With this function, the resistor and the capacitor of an RC series circuit (High pass / low pass) can be calculated with a given impedance and cutoff frequency.

RC impedance calculator

 Input Frequency Hz kHz MHz GHz Impedance mΩ Ω kΩ MΩ Decimal places 0 1 2 3 4 6 8 10 Result Capacitor C Resistors R

### Formulas for calculating R and C

At the cutoff frequency, the reactance of the capacitor is identical to the ohmic resistance.

The formula
$$\displaystyle Z^2 = R^2 + X_C^2$$

can be switched to

$$\displaystyle Z^2 = 2 · R^2$$ oder $$\displaystyle Z = \sqrt{2} · R$$

Calculate resistor : $$\displaystyle R=\frac{Z}{\sqrt{2}}$$

Calculate capacitor : $$\displaystyle C=\frac{1}{2·π·f·X_C} ⇒$$   „ $$\displaystyle \frac{1}{2·π·f·R}$$