Understand the units of measurement used for capacitors. The base unit of capacitance is the Farad (F). This value is too large to be of use in a circuit. Smaller denominations of capacitance are used by electronic circuits.
- Read uF as microFarad. 1 microFarad is 1 times 10 to the -6 power Farad.
- Read pF as picoFarad. 1 picoFarad is 1 times 10 to the -12 power Farad.
Read the value directly on larger bodied capacitors. If the surface of the body is large enough, the value will be printed directly on the capacitor. For example, 47 uF indicates 47 microFarads.
Read the capacitance of smaller bodied capacitors as two or three numbers.The designators uF or pF will not appear due to the small size of the capacitor body.
- Read two-digit numbers as being in picoFarads (pF). For example, 47 would be read as 47 pF.
- Read three-digit numbers as a base capacitance value in picoFarads and a multiplier. The first two digits will indicate the base capacitor value in picoFarads. The third digit will indicate a multiplier to be used on the base number to find the actual value of the capacitor.
- Use the third digit of 0 through 5 to place the corresponding number of 0s behind the base value. The third digit of 8 means multiplies the base value by .01. The third digit of 9 means to multiply the base value by 0.1. For example, 472 would indicate a 4700 pF capacitor and 479 would indicate a 4.7 pF capacitor.
- Digit-Character-Digit. Some small capacitors are marked with codes like 1n0. The digits are the values before and after the decimal point and the character tells you the dimension; so the example given is 1.0 nF (nano-Farad).
Look for a letter code. Some capacitors are defined by a three number code followed by a letter. This letter represents the tolerance of the capacitor, meaning how close the actual value of the capacitor can be expected to be to the indicated value of the capacitor. The tolerances are indicated as follows.
- Read B as 0.10 percent.
- Read C as 0.25 percent.
- Read D as 0.5 percent.
- Read E as 0.5 percent. This is a duplication of a D code.
- Read F as 1 percent.
- Read G as 2 percent.
- Read H as 3 percent.
- Read J as 5 percent.
- Read K as 10 percent.
- Read M as 20 percent.
- Read N as 0.05 percent.
- Read P as plus 100 percent to minus 0 percent.
- Read Z as plus 80 percent to minus 20 percent.