331 capacitor value
330 pF
330 pF · 0.33 nF · 0.00033 µF
| Marked code | 331 |
| Picofarads | 330 pF |
| Nanofarads | 0.33 nF |
| Microfarads | 0.00033 µF |
| Farads | 3.30e-10 F |
Reading the code
The three digits are not a part number. The first two are the value in picofarads and the third says what to do with them:
33 × 101 = 330 pF
So 331 is 33 followed by 1 zero: 330 pF. The code is always in picofarads even when the part is sold in microfarads, which is the whole difficulty with it — a capacitor marked 331 is stocked as 0.00033 µF and the two numbers look nothing alike.
What 330 pF does at frequency
A capacitor's opposition to a signal is its reactance, 1 ÷ (2πfC), and it falls as the frequency rises. Over the range of frequencies a circuit can put across it, a 330 pF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 9.65 MΩ |
| 1 kHz — audio | 482.29 kΩ |
| 100 kHz — switching | 4.82 kΩ |
| 10 MHz — RF | 48.23 Ω |
Ten times the frequency is a tenth of the reactance, every time — which is why choosing a decoupling capacitor is really choosing the frequency band you want it to be low-impedance across, and why boards carry several sizes in parallel rather than one large one.
The letter after the number
A code like 331K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 330 pF means |
|---|---|---|
331J | ±5% | 313.5 pF to 346.5 pF |
331K | ±10% | 297 pF to 363 pF |
331M | ±20% | 264 pF to 396 pF |
331Z | +80% / −20% | 264 pF to 594 pF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 331Z can legitimately be anything from 264 pF to 594 pF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 330 pF turns up
Hundreds of picofarads is filtering at radio frequencies and the timing element in fast oscillators. Below a nanofarad, a ceramic capacitor is close to ideal — very little loss, very little drift — which is why this range is used where accuracy matters.
Frequently asked questions
What is the value of a 331 capacitor?
330 pF — 330 pF · 0.33 nF · 0.00033 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 331 is 33 followed by 1 zero = 330 pF.
What is a 331 capacitor in µF?
0.00033 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 330 pF, 0.33 nF and 0.00033 µF are the same capacitor written three ways.
What does the letter after 331 mean?
Tolerance. 331K is ±10%, 331J is ±5% and 331M is ±20% — so a 331K is anywhere from 297 pF to 363 pF and still in specification. A Z means +80%/−20%, which is not a mistake: some ceramic dielectrics really are that loose.
What is the impedance of a 331 capacitor at 1 kHz?
482.29 kΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 4.82 kΩ at 100 kHz and 48.23 Ω at 10 MHz.
Nearby codes
- 391 capacitor — 390 pF
- 471 capacitor — 470 pF
- 561 capacitor — 560 pF
- 681 capacitor — 680 pF
- 821 capacitor — 820 pF
- 102 capacitor — 1 nF
- 122 capacitor — 1.2 nF
- 152 capacitor — 1.5 nF
- 182 capacitor — 1.8 nF
- 222 capacitor — 2.2 nF