When constructing electronic projects or repairing faulty items it will be necessary to determine the exact value of capacitors, which sometimes have confusing numbers on them. I have put together this page for Capacitors and this page for Resistors to help identify their values.
Most Electrolytic capacitors are clearly marked with the value of the capacitor in microfarads (μF), the polarity of the leads, and the working voltage. For this reason electrolytic capacitors are often the easiest capacitors to identify and use. They will have clearly printed on the body something like: 220μF 50volts and have a (usually white) stripe down one side with a -ve sign to indicate that lead is to go only to the negative side of the circuit.
Many circuits specify small capacitors, with polystyrene, polyester and ceramic capacitors being popular choices. Some circuits may specify capacitor values in microfarads (μF), some in nanofarads (nF) while others may use picofarads (pF) which can all be rather confusing.
Often the capacitor will simply be marked with a two digit number printed on the body such as "10" for example. This indicates that it is a 10pF capacitor. However you may find some capacitors marked "10n" and this capacitor will have a value of 10nF (ie 10,000pF), this is sometimes seen on polystyrene types and some resin dipped ceramics.
To make matters rather more confusing, when we eventually arrive home with a plastic bag full of components keen to construct a circuit we find that many capacitors are marked with a three digit code such as "103" or "104" and some others have a three digit code plus a letter on the end such as "101K" or "102K".
The capacitors marked with three digits are similar to resistors in that the first two digits represent the value in pF (as above) and the third digit is the multiplier with a letter to indicate the Tolerance. So "100" would be 10pF multiplied by zero i.e. 10pF. "103" is 10pF multiplied by 1000 ie 10,000pF or to put is another way 0.01 microfarads. "471K" would be a 470pF capacitor with a 10% Tolerance.
Confused? Help is at hand.To help make sense of all this and to be able to easily convert from nF to pF to uF etc. here are a couple of handy tables:
|CODE / Marking||μF|
|Capacitor Tolerance Table.|
103K = 0.01μF i.e 10nF with 10% Tolerance.
104K = 0.1μF i.e. 100nF with 10% Tolerance.
Or better still this page will do it for you!
It is quite unusual to find capacitors with colour codes but sometimes you may run across polyester caps that are marked with coloured stripes rather than numbers.
Below is the colour code for these capacitors. The value will be in picofarads (pF).
(away from leads)
(closest to leads)
|YELLOW||4||4||x 0.01µf||---||400 Vdc|
|More on voltage markings.|
Although this information is not entirely confirmed, some capacitors may have voltage indicated by a letter, as in the table below:
|D = 16 volts||Q = 500 volts||U = 4000 volts|
|F = 25 volts||R = 1000 volts||W = 5000 volts|
|H = 50 volts||S = 2000 volts||X = 6000 volts|
|K = 100 volts||T = 3000 volts||Y = 7500 volts|