186 capacitor value
18 µF
18,000,000 pF · 18000 nF · 18 µF
| Marked code | 186 |
| Picofarads | 18,000,000 pF |
| Nanofarads | 18000 nF |
| Microfarads | 18 µF |
| Farads | 1.80e-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:
18 × 106 = 18,000,000 pF
So 186 is 18 followed by 6 zeros: 18,000,000 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 186 is stocked as 18 µF and the two numbers look nothing alike.
What 18 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 18 µF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 176.84 Ω |
| 1 kHz — audio | 8.84 Ω |
| 100 kHz — switching | 88.4 mΩ |
| 10 MHz — RF | 0.9 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 186K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 18 µF means |
|---|---|---|
186J | ±5% | 17.1 µF to 18.9 µF |
186K | ±10% | 16.2 µF to 19.8 µF |
186M | ±20% | 14.4 µF to 21.6 µF |
186Z | +80% / −20% | 14.4 µF to 32.4 µF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 186Z can legitimately be anything from 14.4 µF to 32.4 µF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 18 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 186 capacitor?
18 µF — 18,000,000 pF · 18000 nF · 18 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 186 is 18 followed by 6 zeros = 18,000,000 pF.
What is a 186 capacitor in µF?
18 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 18,000,000 pF, 18000 nF and 18 µF are the same capacitor written three ways.
What does the letter after 186 mean?
Tolerance. 186K is ±10%, 186J is ±5% and 186M is ±20% — so a 186K is anywhere from 16.2 µF to 19.8 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 186 capacitor at 1 kHz?
8.84 Ω. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 88.4 mΩ at 100 kHz and 0.9 mΩ at 10 MHz.
Nearby codes
- 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
- 108 capacitor — 0.1 pF
- 128 capacitor — 0.12 pF