681 capacitor value
680 pF
680 pF · 0.68 nF · 0.00068 µF
| Marked code | 681 |
| Picofarads | 680 pF |
| Nanofarads | 0.68 nF |
| Microfarads | 0.00068 µF |
| Farads | 6.80e-10 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 × 101 = 680 pF
So 681 is 68 followed by 1 zero: 680 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 681 is stocked as 0.00068 µF and the two numbers look nothing alike.
What 680 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 680 pF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 4.68 MΩ |
| 1 kHz — audio | 234.05 kΩ |
| 100 kHz — switching | 2.34 kΩ |
| 10 MHz — RF | 23.41 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 681K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 680 pF means |
|---|---|---|
681J | ±5% | 646 pF to 714 pF |
681K | ±10% | 612 pF to 748 pF |
681M | ±20% | 544 pF to 816 pF |
681Z | +80% / −20% | 544 pF to 1.224 nF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 681Z can legitimately be anything from 544 pF to 1.224 nF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 680 pF turns up
Hundreds of picofarads is filtering at radio frequencies and the timing element in fast oscillators. Below a nanofarad, a ceramic capacitor is close to ideal — very little loss, very little drift — which is why this range is used where accuracy matters.
Frequently asked questions
What is the value of a 681 capacitor?
680 pF — 680 pF · 0.68 nF · 0.00068 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 681 is 68 followed by 1 zero = 680 pF.
What is a 681 capacitor in µF?
0.00068 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 680 pF, 0.68 nF and 0.00068 µF are the same capacitor written three ways.
What does the letter after 681 mean?
Tolerance. 681K is ±10%, 681J is ±5% and 681M is ±20% — so a 681K is anywhere from 612 pF to 748 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 681 capacitor at 1 kHz?
234.05 kΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 2.34 kΩ at 100 kHz and 23.41 Ω at 10 MHz.
Nearby codes
- 821 capacitor — 820 pF
- 102 capacitor — 1 nF
- 122 capacitor — 1.2 nF
- 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