Capacitance:

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