688 capacitor value
0.68 pF
0.68 pF · 0.0007 nF · 0.000001 µF
| Marked code | 688 |
| Picofarads | 0.68 pF |
| Nanofarads | 0.0007 nF |
| Microfarads | 0.000001 µF |
| Farads | 6.80e-13 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:
68 × 0.01 = 0.68 pF
The last digit here is 8, which is one of the two exceptions. Eight and nine do not mean 10⁸ and 10⁹ — they mean × 0.01 and × 0.1, and they exist so that values below ten picofarads can be written in the same three characters. Read literally, 688 would be 68 × 108 = 6,800 µF, which is not a ceramic capacitor and not what is in your hand.
What 0.68 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 0.68 pF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 4.68 GΩ |
| 1 kHz — audio | 234.05 MΩ |
| 100 kHz — switching | 2.34 MΩ |
| 10 MHz — RF | 23.41 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 688K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 0.68 pF means |
|---|---|---|
688J | ±5% | 0.65 pF to 0.71 pF |
688K | ±10% | 0.61 pF to 0.75 pF |
688M | ±20% | 0.54 pF to 0.82 pF |
688Z | +80% / −20% | 0.54 pF to 1.22 pF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 688Z can legitimately be anything from 0.54 pF to 1.22 pF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 0.68 pF turns up
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Frequently asked questions
What is the value of a 688 capacitor?
0.68 pF — 0.68 pF · 0.0007 nF · 0.000001 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 688 is 68 followed by a divide rather than a multiply: 68 × 0.01 = 0.68 pF.
What is a 688 capacitor in µF?
0.000001 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 0.68 pF, 0.0007 nF and 0.000001 µF are the same capacitor written three ways.
What does the letter after 688 mean?
Tolerance. 688K is ±10%, 688J is ±5% and 688M is ±20% — so a 688K is anywhere from 0.61 pF to 0.75 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 688 capacitor at 1 kHz?
234.05 MΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 2.34 MΩ at 100 kHz and 23.41 kΩ at 10 MHz.
Nearby codes
- 828 capacitor — 0.82 pF
- 109 capacitor — 1 pF
- 129 capacitor — 1.2 pF
- 159 capacitor — 1.5 pF
- 189 capacitor — 1.8 pF
- 229 capacitor — 2.2 pF
- 279 capacitor — 2.7 pF
- 339 capacitor — 3.3 pF
- 399 capacitor — 3.9 pF
- 479 capacitor — 4.7 pF