183 capacitor value
18 nF
18,000 pF · 18 nF · 0.018 µF
| Marked code | 183 |
| Picofarads | 18,000 pF |
| Nanofarads | 18 nF |
| Microfarads | 0.018 µF |
| Farads | 1.80e-8 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 × 103 = 18,000 pF
So 183 is 18 followed by 3 zeros: 18,000 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 183 is stocked as 0.018 µF and the two numbers look nothing alike.
What 18 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 18 nF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 176.84 kΩ |
| 1 kHz — audio | 8.84 kΩ |
| 100 kHz — switching | 88.42 Ω |
| 10 MHz — RF | 884.2 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 183K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 18 nF means |
|---|---|---|
183J | ±5% | 17.1 nF to 18.9 nF |
183K | ±10% | 16.2 nF to 19.8 nF |
183M | ±20% | 14.4 nF to 21.6 nF |
183Z | +80% / −20% | 14.4 nF to 32.4 nF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 183Z can legitimately be anything from 14.4 nF to 32.4 nF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 18 nF turns up
Tens of nanofarads is coupling between audio stages and the smaller decoupling capacitors on a logic board. A 10 nF part alongside a 100 nF one is a common pairing, the smaller of the two handling the frequencies the larger one is too slow for.
Frequently asked questions
What is the value of a 183 capacitor?
18 nF — 18,000 pF · 18 nF · 0.018 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 183 is 18 followed by 3 zeros = 18,000 pF.
What is a 183 capacitor in µF?
0.018 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 18,000 pF, 18 nF and 0.018 µF are the same capacitor written three ways.
What does the letter after 183 mean?
Tolerance. 183K is ±10%, 183J is ±5% and 183M is ±20% — so a 183K is anywhere from 16.2 nF to 19.8 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 183 capacitor at 1 kHz?
8.84 kΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 88.42 Ω at 100 kHz and 884.2 mΩ at 10 MHz.
Nearby codes
- 223 capacitor — 22 nF
- 273 capacitor — 27 nF
- 333 capacitor — 33 nF
- 393 capacitor — 39 nF
- 473 capacitor — 47 nF
- 563 capacitor — 56 nF
- 683 capacitor — 68 nF
- 823 capacitor — 82 nF
- 104 capacitor — 100 nF
- 124 capacitor — 120 nF