Reading capacitor markings
Ceramic capacitors are too small to print a full value on, so manufacturers use a short code instead. Most use the three-digit EIA system, which gives the capacitance in picofarads (pF), much like the color bands on a resistor.
The three-digit code
The first two digits are the significant figures and the third is the number of zeros to add. The result is in picofarads.
104= 10 followed by four zeros = 100,000 pF = 100 nF = 0.1 µF472= 47 followed by two zeros = 4,700 pF = 4.7 nF220= 22 followed by no zeros = 22 pF
A third digit of 8 or 9 means multiply by 0.01 or 0.1, which is rare. A 7 only turns up on large multilayer ceramic and tantalum parts, where 107 means 100 µF. Values under 100 pF are often printed directly, so a capacitor marked 22 is simply 22 pF.
Letters in the code
An R marks the decimal point for values under 10 pF: 4R7 is 4.7 pF. On film capacitors and larger parts you may see n or u used the same way, so 4n7 is 4.7 nF and 1u0 is 1 µF.
Tolerance letters
| Letter | Tolerance |
|---|---|
| B | ±0.1 pF |
| C | ±0.25 pF |
| D | ±0.5 pF |
| F | ±1% |
| G | ±2% |
| H | ±3% |
| J | ±5% |
| K | ±10% |
| M | ±20% |
| P | +100% / −0% |
| Z | +80% / −20% |
B, C and D are absolute tolerances used on small capacitors, typically below 10 pF. Z is common on cheap high-capacitance ceramics, whose value can be far above nominal.
Voltage codes
Some capacitors carry a digit and letter in front of the value, such as 2A104J. The prefix is the rated voltage: 1H is 50 V, 2A is 100 V, 2E is 250 V and 2J is 630 V. Many small ceramic disc capacitors show the voltage as a plain number instead, such as 50V or 1KV.
Real capacitance can differ
High-capacitance ceramics with Y5V or X7R dielectrics lose part of their capacitance as the applied DC voltage rises and as the temperature changes. For timing or filter circuits that need a stable value, choose C0G (NP0) parts, which barely drift.
