RC Circuits: Charge/Discharge Time & Capacitors/Resistances

[zvee_y]

In RC circuit, what is the mathematic relationship between the time of charge or dischare and the capacitors ? time of charge or discharge andn the resistances?
I know that as the capacitor or the resistance is increased, the time it take to charge is also increase as well.
But I am not sure about the mathematic relationship though. Please help me out guys!

 

[berkeman]

The "RC Time Constant" ratios directly with both R and C:

http://en.wikipedia.org/wiki/RC_time_constant

 

[mikelepore]

There's an irrational number e which has a value close to 2.718 . It's the base of natural logarithms. The time constant RC is the time required for a capacitor C that is charging or discharging through a resistor R to reach the fraction (1/e) of its final value.