120 capacitor value
12 pF
12 pF · 0.012 nF · 0.000012 µF
| Marked code | 120 |
| Picofarads | 12 pF |
| Nanofarads | 0.012 nF |
| Microfarads | 0.000012 µF |
| Farads | 1.20e-11 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:
12 × 100 = 12 pF
So 120 is 12 followed by 0 zeros: 12 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 120 is stocked as 0.000012 µF and the two numbers look nothing alike.
What 12 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 12 pF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 265.26 MΩ |
| 1 kHz — audio | 13.26 MΩ |
| 100 kHz — switching | 132.63 kΩ |
| 10 MHz — RF | 1.33 kΩ |
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 120K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 12 pF means |
|---|---|---|
120J | ±5% | 11.4 pF to 12.6 pF |
120K | ±10% | 10.8 pF to 13.2 pF |
120M | ±20% | 9.6 pF to 14.4 pF |
120Z | +80% / −20% | 9.6 pF to 21.6 pF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 120Z can legitimately be anything from 9.6 pF to 21.6 pF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 12 pF turns up
Tens of picofarads is the crystal load range: the two capacitors either side of a quartz crystal that set it oscillating at its marked frequency. Also RF tuning and the compensation capacitor round a fast op-amp.
Frequently asked questions
What is the value of a 120 capacitor?
12 pF — 12 pF · 0.012 nF · 0.000012 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 120 is 12 followed by 0 zeros = 12 pF.
What is a 120 capacitor in µF?
0.000012 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 12 pF, 0.012 nF and 0.000012 µF are the same capacitor written three ways.
What does the letter after 120 mean?
Tolerance. 120K is ±10%, 120J is ±5% and 120M is ±20% — so a 120K is anywhere from 10.8 pF to 13.2 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 120 capacitor at 1 kHz?
13.26 MΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 132.63 kΩ at 100 kHz and 1.33 kΩ at 10 MHz.
Nearby codes
- 150 capacitor — 15 pF
- 180 capacitor — 18 pF
- 220 capacitor — 22 pF
- 270 capacitor — 27 pF
- 330 capacitor — 33 pF
- 390 capacitor — 39 pF
- 470 capacitor — 47 pF
- 560 capacitor — 56 pF
- 680 capacitor — 68 pF
- 820 capacitor — 82 pF