Voltage and charge are related but different as has been pointed out.
Here is a non-math way of understanding this...
I have two compressors running that are delivering the same flow (in cubic centimeters per/minute) of air into two compressed air cylinders.
The two cylinders are different sizes. One is twice as big as the other in VOLUME. It will hold twice as much air....but this is KEY, twice as much air at THE SAME PRESSURE. If the cylinders are said to be "empty", they actually DO have air in them, only at atmospheric pressure (equalized).
Turn on the compressors. It will take TWICE AS LONG for the larger cylinder to reach the same pressure as the small one, despite having the same flow of air going in.
So a STORED CYLINDER (think capacitor) which is twice as big at X pressure has twice the number of air molecules as a half size cylinder at the same pressure.
A large capacitor holding x number of NEGATIVELY CHARGED PARTICLES will be HALF THE VOLTAGE of a capacitor that is half its size with the same number (x) of charged particles.
If the Larger capacitor is fully charged to twice the charge of the smaller capacitor, they will have the same voltage.
Voltage is PRESSURE.
Charge is unit per area/volume...as a percentage of capacity given a certain pressure.
It is really easy when you think of it this way.