Small ceramic capacitors are too tiny to print a full value on, so they use a compact 3-digit code — the same idea as resistor colour codes, but in digits. Once you know the rule, a marking like 104 or 473 decodes in seconds.
The 3-digit code
The code works exactly like the resistor system, and the result is always in picofarads (pF):
- The first two digits are the significant figures.
- The third digit is the multiplier — the number of zeros to add.
So 104 is 10 followed by 4 zeros = 100,000 pF. From there you convert into friendlier units.
Picofarads, nanofarads, microfarads
Capacitance is quoted in three units that each differ by a factor of 1,000:
| Unit | Symbol | In picofarads |
|---|---|---|
| Picofarad | pF | 1 |
| Nanofarad | nF | 1,000 |
| Microfarad | µF | 1,000,000 |
So that 104 capacitor is 100,000 pF = 100 nF = 0.1 µF — one of the most common decoupling capacitors in all of electronics.
Worked examples
473→ 47 + 3 zeros = 47,000 pF = 47 nF222→ 22 + 2 zeros = 2,200 pF = 2.2 nF101→ 10 + 1 zero = 100 pF331→ 33 + 1 zero = 330 pF
22 or 4.7 is 22 pF or 4.7 pF — if there is no third digit acting as a multiplier, read it literally.The tolerance letter
A letter after the digits gives the tolerance — how much the actual capacitance may differ from the marked value:
| Letter | Tolerance |
|---|---|
J | ±5% |
K | ±10% |
M | ±20% |
Z | +80% / −20% |
So 104K is 100 nF at ±10%. For decoupling and filtering this loose tolerance is fine; for timing or tuned circuits you want tighter parts.
Voltage rating
The code says nothing about the voltage rating — the maximum voltage the capacitor can safely take. That is printed separately (e.g. 50V, 2kV) or implied by the part series. Always choose a capacitor rated comfortably above the voltage in your circuit; exceeding it can cause the dielectric to break down.
Polarity: which way round?
Some capacitors care about direction and some do not, and getting it wrong can be destructive. Electrolytic and tantalum capacitors are polarised: one terminal must connect to the more positive side of the circuit. They are marked accordingly — electrolytics have a stripe on the negative side and the longer leg is positive; tantalums mark the positive terminal. Wire one in backwards and it can heat up, leak, or pop. Ceramic and film capacitors are non-polarised and can go in either way, which is part of why the little disc ceramics with the 3-digit code are so common.
Choosing the right type
The code tells you the value, but the type matters too. Ceramics are cheap, small and great for decoupling and high frequencies, though their value can drift with temperature and voltage. Film capacitors are stable and accurate, ideal for timing and audio. Electrolytics give large values cheaply for power-supply smoothing, at the cost of size, polarity and a shorter life. Matching the type to the job is as important as getting the value right — a tuned circuit needs a stable film part, while a power rail just needs bulk capacitance from an electrolytic.
Decode it instantly
The Capacitor Code Calculator converts any code to pF, nF, and µF with its tolerance, and works in reverse too. For the closely-related resistor system, see how to read resistor colour codes.
Frequently asked questions
What does a code like 104 mean on a capacitor?
It reads like resistor codes: the first two digits are significant figures and the third is the number of zeros, giving a value in picofarads. 104 = 10 followed by 4 zeros = 100,000 pF = 100 nF = 0.1 µF.
Why are capacitor values given in picofarads?
The 3-digit code is always in picofarads (pF) by convention, because it keeps the numbers as whole digits. You then convert up to nanofarads or microfarads as needed.
What does the letter after the number mean?
It is the tolerance — how far the real value may stray from the marked one. For example J = ±5%, K = ±10%, M = ±20%.
How do I read the voltage rating?
On small ceramic capacitors the voltage is often not printed at all — you rely on the part’s datasheet or markings. On larger film and electrolytic capacitors the working voltage is printed directly (e.g. 25V, 400V). Always choose a capacitor rated comfortably above the highest voltage it will see, or it can fail.
Why do some capacitors have a stripe or a minus sign?
That marks polarity. Electrolytic and tantalum capacitors are polarised — one lead must go to the more positive side. The stripe (or shorter leg) marks the negative terminal. Connecting one backwards can make it fail, sometimes dramatically. Ceramic and film capacitors are non-polarised and can go either way.
What is the difference between pF, nF and µF?
They are just scale steps: 1 µF = 1,000 nF = 1,000,000 pF. The 3-digit code is always in pF, so you convert up: 104 = 100,000 pF = 100 nF = 0.1 µF. Datasheets and schematics may use any of the three, so being able to convert between them quickly is essential.