If we increase the voltage between the plates, the charge increases, but the ratio of charge to voltage remains the same. This ratio gives the capacitance (C) of the capacitor.
Charge/Voltage = A constant called capacitance
When the charge (Q) is in coulombs and the voltage (V) in volts, then the capacitance (C) is in farads (F).
C =Q/V (and also Q = VC, V = Q/C)
A capacitor has a capacitance of one Farad when a charging current of one ampere, flowing for one second, causes a change of voltage of one volt between its plates. The Farad is a huge unit and smaller units are used in practice.
1 microfarad (μF) = 10-6 farad
1 picofarad (pF) = 10-12 farad