Calculate capacitance i.a. via reactive power
From impedance of capacitor $$Z_{c}=\frac{1}{j\omega C}$$, then the reactance is $$X{c}=\frac{1}{\omega C}$$ and reactive power is $$Q=I^2 X=\frac{U^2}{X}=\frac{I^2}{\omega C}$$ $$C=\frac{I^2}{\omega Q}$$