Xrated Capacitor

Unlike electrolytic capacitors the value you see written on x-rated capacitors is not the actual capacitance value, it is kind of coded (for reason I don't know) on the capacitor written in format similar to the one below
225J 400v. 400v tells the maximum charging voltage of the capacitor.
Electrolytic (47uf)

X-rated capacitor (2.2uf)

Decoding the actual is easy with the value above. You just write out the first two digits(22) and multiply 10 raised to the power of the third digit (5)

22*10^5 = 2200000pf

Note: the value above is in picofarads to get the equivalent in microfarads you divide by 1000000.

2200000/1000000= 2.2uf

Now over to the letter 'J', it signifies the tolerance of the capacitor in this case the tolerance is 5%.

F = 1%
G =2%
H=3%
J=5%
List of common Capacitors