101 capacitor value
100 pF
100 pF · 0.1 nF · 0.0001 µF
| Marked code | 101 |
| Picofarads | 100 pF |
| Nanofarads | 0.1 nF |
| Microfarads | 0.0001 µF |
| Farads | 1.00e-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:
10 × 101 = 100 pF
So 101 is 10 followed by 1 zero: 100 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 101 is stocked as 0.0001 µF and the two numbers look nothing alike.
What 100 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 100 pF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 31.83 MΩ |
| 1 kHz — audio | 1.59 MΩ |
| 100 kHz — switching | 15.92 kΩ |
| 10 MHz — RF | 159.15 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 101K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 100 pF means |
|---|---|---|
101J | ±5% | 95 pF to 105 pF |
101K | ±10% | 90 pF to 110 pF |
101M | ±20% | 80 pF to 120 pF |
101Z | +80% / −20% | 80 pF to 180 pF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 101Z can legitimately be anything from 80 pF to 180 pF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 100 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 101 capacitor?
100 pF — 100 pF · 0.1 nF · 0.0001 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 101 is 10 followed by 1 zero = 100 pF.
What is a 101 capacitor in µF?
0.0001 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 100 pF, 0.1 nF and 0.0001 µF are the same capacitor written three ways.
What does the letter after 101 mean?
Tolerance. 101K is ±10%, 101J is ±5% and 101M is ±20% — so a 101K is anywhere from 90 pF to 110 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 101 capacitor at 1 kHz?
1.59 MΩ. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 15.92 kΩ at 100 kHz and 159.15 Ω at 10 MHz.
Nearby codes
- 121 capacitor — 120 pF
- 151 capacitor — 150 pF
- 181 capacitor — 180 pF
- 221 capacitor — 220 pF
- 271 capacitor — 270 pF
- 331 capacitor — 330 pF
- 391 capacitor — 390 pF
- 471 capacitor — 470 pF
- 561 capacitor — 560 pF
- 681 capacitor — 680 pF