Capacitive reactance is the opposition to the change of voltage across an element. The reactance gets larger if the frequency and capacitance get smaller.
The reactance can be calculated with the formula below. The reactance is positive in these formulas, so you have to add a negative sign when you want to calculate the impedance.
f is the symbol for frequency and is measured in hertz (Hz).
C is the symbol for capacitance and is measured in farad (F).
X C is the symbol for capacitive reactance and is measured in (Ω).