Parallel Capacitor Calculator
Check out this parallel capacitor calculator to evaluate the resulting capacity in this kind of circuit.
The formula
series and parallel combination — capacitors work the opposite way
Capacitors are the exception
Resistors and inductors add in series and combine reciprocally in parallel. Capacitors do exactly the reverse: they add in parallel and combine reciprocally in series.
It is not arbitrary. What actually adds in series is always impedance, and a capacitor's impedance is inversely proportional to its capacitance. Adding impedances in series therefore means adding reciprocals of capacitance, which is where the apparent inversion comes from. Physically, putting capacitors in series is like making the dielectric thicker, which reduces capacitance; putting them in parallel is like making the plates bigger, which increases it.
Two useful consequences. Whenever reciprocals add, the total is always smaller than the smallest individual component, and n identical components give exactly one nth of a single value. That gives you a quick sanity check: a parallel resistance larger than any of its resistors is an arithmetic error.