100 nF capacitor (0.1 µF)
A 100 nF capacitor is the same as 0.1 µF or 100,000 pF. On ceramic and film parts it is printed as the code 104; schematics often write 100n.
How a 100 nF capacitor is marked
| Style | Marking | Where you see it |
|---|---|---|
| 3-digit code | 104 | Ceramic discs, multilayer ceramics, film capacitors |
| Code + tolerance | 104J · 104K · 104M | ±5% · ±10% · ±20% |
| Code + voltage | 1H104K · 2A104J | 50 V · 100 V film capacitors |
| IEC 60062 letter code | 100n | Schematics, European parts (the letter is the decimal point) |
| Plain value | .1 or 0.1 (µF) | Older US parts and electrolytics — bare decimals are µF |
| SMD (0402–1206) | usually unmarked | Check the reel label or measure with an LCR meter |
100 nF in every unit
| Picofarads | 100,000 pF |
|---|---|
| Nanofarads | 100 nF |
| Microfarads | 0.1 µF |
| Farads | 1 × 10^-7 |
Reactance of 100 nF
A capacitor's opposition to AC falls as frequency rises: XC = 1 ÷ (2π f C). This tells you whether 100 nF passes or blocks a signal — a decoupling capacitor needs a low reactance at the noise frequency, a coupling capacitor at the lowest signal frequency.
| Frequency | Reactance XC |
|---|---|
| 50 Hz | 31.8 kΩ |
| 60 Hz | 26.5 kΩ |
| 1 kHz | 1.59 kΩ |
| 10 kHz | 159 Ω |
| 100 kHz | 15.9 Ω |
| 1 MHz | 1.59 Ω |
| 10 MHz | 0.159 Ω |
Real capacitors stop behaving like ideal ones above their self-resonant frequency, which depends on the package and lead length, so treat the high-frequency rows as an upper bound on performance.
RC time constant and filter corner with 100 nF
With a resistor R, the capacitor charges to 63% in one time constant τ = R × C and to over 99% in 5τ. The same pair makes a first-order low-pass or high-pass filter with corner frequency fc = 1 ÷ (2π R C).
| Resistor | τ = RC | 5τ (≈ full charge) | Corner fc |
|---|---|---|---|
| 100 Ω | 10 µs | 50 µs | 15.9 kHz |
| 1 kΩ | 100 µs | 500 µs | 1.59 kHz |
| 10 kΩ | 1 ms | 5 ms | 159 Hz |
| 100 kΩ | 10 ms | 50 ms | 15.9 Hz |
Choosing a 100 nF capacitor
| Usual dielectric | X7R ceramic (0402–1206 SMD or 2.54 mm radial) |
|---|---|
| Common voltage ratings | 16–50 V |
| Neighbouring E6 values | 33 nF, 47 nF, 68 nF, 150 nF, 220 nF, 330 nF |
100 nF is the standard decoupling capacitor placed beside the supply pin of nearly every IC. It is the same part whether the drawing says 100nF, 0.1µF or 104. X7R is the usual dielectric; put it as close to the pin as possible and add a larger bulk capacitor (1–10 µF) per board or rail.
FAQ
What is the code for a 100 nF capacitor?
104. The first two digits (10) are picofarads and the third (4) is the number of zeros: 100,000 pF. In IEC letter notation it is written 100n.
Is 100 nF the same as 0.1 µF?
Yes. 100,000 pF = 100 nF = 0.1 µF; they are three names for the same capacitance.
What is the reactance of a 100 nF capacitor?
Xc = 1 ÷ (2π × f × C). At 1 kHz a 100 nF capacitor has 1.59 kΩ; at 50 Hz 31.8 kΩ.
What cutoff frequency does 100 nF give with 10 kΩ?
fc = 1 ÷ (2π × 10 kΩ × 100 nF) = 159 Hz, and the time constant τ = R × C = 1 ms.