126 capacitor value
12 µF
12,000,000 pF · 12000 nF · 12 µF
| Marked code | 126 |
| Picofarads | 12,000,000 pF |
| Nanofarads | 12000 nF |
| Microfarads | 12 µF |
| Farads | 1.20e-5 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 × 106 = 12,000,000 pF
So 126 is 12 followed by 6 zeros: 12,000,000 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 126 is stocked as 12 µF and the two numbers look nothing alike.
What 12 µF 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 µF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 265.26 Ω |
| 1 kHz — audio | 13.26 Ω |
| 100 kHz — switching | 132.6 mΩ |
| 10 MHz — RF | 1.3 mΩ |
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 126K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 12 µF means |
|---|---|---|
126J | ±5% | 11.4 µF to 12.6 µF |
126K | ±10% | 10.8 µF to 13.2 µF |
126M | ±20% | 9.6 µF to 14.4 µF |
126Z | +80% / −20% | 9.6 µF to 21.6 µF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 126Z can legitimately be anything from 9.6 µF to 21.6 µF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 12 µF turns up
Microfarads and up is bulk energy storage: holding a rail up between switching cycles, smoothing a supply, or coupling a signal that goes down to a few hertz. Above about 10 µF ceramics give way to electrolytics and tantalums, which is why the code runs out here.
Frequently asked questions
What is the value of a 126 capacitor?
12 µF — 12,000,000 pF · 12000 nF · 12 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 126 is 12 followed by 6 zeros = 12,000,000 pF.
What is a 126 capacitor in µF?
12 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 12,000,000 pF, 12000 nF and 12 µF are the same capacitor written three ways.
What does the letter after 126 mean?
Tolerance. 126K is ±10%, 126J is ±5% and 126M is ±20% — so a 126K is anywhere from 10.8 µF to 13.2 µF 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 126 capacitor at 1 kHz?
13.26 Ω. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 132.6 mΩ at 100 kHz and 1.3 mΩ at 10 MHz.
Nearby codes
- 156 capacitor — 15 µF
- 186 capacitor — 18 µF
- 226 capacitor — 22 µF
- 276 capacitor — 27 µF
- 336 capacitor — 33 µF
- 396 capacitor — 39 µF
- 476 capacitor — 47 µF
- 566 capacitor — 56 µF
- 686 capacitor — 68 µF
- 826 capacitor — 82 µF