122 capacitor value
1.2 nF
1,200 pF · 1.2 nF · 0.0012 µF
| Marked code | 122 |
| Picofarads | 1,200 pF |
| Nanofarads | 1.2 nF |
| Microfarads | 0.0012 µF |
| Farads | 1.20e-9 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 × 102 = 1,200 pF
So 122 is 12 followed by 2 zeros: 1,200 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 122 is stocked as 0.0012 µF and the two numbers look nothing alike.
What 1.2 nF 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 1.2 nF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 2.65 MΩ |
| 1 kHz — audio | 132.63 kΩ |
| 100 kHz — switching | 1.33 kΩ |
| 10 MHz — RF | 13.26 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 122K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 1.2 nF means |
|---|---|---|
122J | ±5% | 1.14 nF to 1.26 nF |
122K | ±10% | 1.08 nF to 1.32 nF |
122M | ±20% | 960 pF to 1.44 nF |
122Z | +80% / −20% | 960 pF to 2.16 nF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 122Z can legitimately be anything from 960 pF to 2.16 nF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 1.2 nF turns up
Single-figure nanofarads is audio filtering and snubbing across switch contacts. It is also the range where a capacitor stops being a precision component and starts being a bypass, depending on the dielectric it is made from.
Frequently asked questions
What is the value of a 122 capacitor?
1.2 nF — 1,200 pF · 1.2 nF · 0.0012 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 122 is 12 followed by 2 zeros = 1,200 pF.
What is a 122 capacitor in µF?
0.0012 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 1,200 pF, 1.2 nF and 0.0012 µF are the same capacitor written three ways.
What does the letter after 122 mean?
Tolerance. 122K is ±10%, 122J is ±5% and 122M is ±20% — so a 122K is anywhere from 1.08 nF to 1.32 nF 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 122 capacitor at 1 kHz?
132.63 kΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 1.33 kΩ at 100 kHz and 13.26 Ω at 10 MHz.
Nearby codes
- 152 capacitor — 1.5 nF
- 182 capacitor — 1.8 nF
- 222 capacitor — 2.2 nF
- 272 capacitor — 2.7 nF
- 332 capacitor — 3.3 nF
- 392 capacitor — 3.9 nF
- 472 capacitor — 4.7 nF
- 562 capacitor — 5.6 nF
- 682 capacitor — 6.8 nF
- 822 capacitor — 8.2 nF