You must know these number from the original capacitor:
Capacitance Value – This is the most important value, in micro Farads because it determines to frequency that the capacitor acts as a high-pass filter. Usually micro Farad is abbreviated as µF or uF, and sometimes mF as (microF). The Greek letter mu means one millionth of a Farad. uF is often used when someone can't type out the Greek letter µ. mF is confusing because mF also means milli Farad, 1,000 µF = 1 mF.
Capacitance Value is usually accompanied by a ±% tolerance value, such as 7µF ± 10%. That cap has been tested to perform anywhere between 6.3 µF and 7.7 µF.Voltage Rating – The highest voltage at which the cap is tested to not fail. Not critical as long as it's greater than about 100V.