Circuit symbol: 
Polarised (1µF +) |
Unpolarised (up to 1µF) |
Real Values (E3 & E6 series)
Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):
Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!
There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.
Examples:
Circuit symbol:
There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.
It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. It the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.
Modern tantalum bead capacitors are printed with their capacitance and
voltage in full. However older ones use a colour-code system which has
two stripes (for the two digits) and a spot of colour for the number of zeros
to give the value in µF. The standard colour code
is used, but for the spot, grey is used to mean × 0.01 and
white means × 0.1 so that values of less than 10µF can be shown.
A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V,
green 16V, blue 20V, grey 25V, white 30V, pink 35V).
For example: blue, grey, black spot means 68µF
For example: blue, grey, white spot means 6.8µF
For example: blue, grey, grey spot means 0.68µF
Circuit symbol: 
Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labelling systems!
Many small value capacitors have their value printed but without a multiplier, so you need to
use experience to work out what the multiplier should be!
For example 0.1 means 0.1µF = 100nF.
Sometimes the multiplier is used in place of the decimal point:
For example: 4n7 means 4.7nF.
For example: 472J means 4700pF = 4.7nF (J means 5% tolerance).
| Colour | Number |
| Black | |
| Brown | |
| Red | |
| Orange | |
| Yellow | |
| Green | |
| Blue | |
| Violet | |
| Grey | |
| White | |
For example:
brown, black, orange means 10000pF = 10nF = 0.01µF.
Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.
For example:
wide red, yellow means 220nF = 0.22µF.
This type is rarely used now. Their value (in pF) is normally printed without units.
Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!)
so you should use a heatsink (such as a crocodile clip). Clip the heatsink to the lead
between the capacitor and the joint.
Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy.
To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.
The E3 series (3 values for each multiple of ten)
10, 22, 47, ... then it continues 100, 220, 470, 1000, 2200, 4700, 10000 etc.
Notice how the step size increases as the value increases (values roughly double each time).
The E6 series (6 values for each multiple of ten)
10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc.
Notice how this is the E3 series with an extra value in the gaps.
The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values.
