⚡ Capacitance Unit Converter
Convert between farads and common sub-units (mF, µF, nF, pF, fF). Supports suffixes like 4.7u, scientific notation like 1e-6, and plain numbers.
Capacitance Converter Tool
Result: -
F, m (mF), u/µ (µF), n (nF), p (pF), f (fF). Examples: 470n, 0.1u, 1e-12.
| Unit | Symbol | Multiplier |
|---|---|---|
| Farad | F | 1 |
| Millifarad | mF | 10⁻³ |
| Microfarad | µF | 10⁻⁶ |
| Nanofarad | nF | 10⁻⁹ |
| Picofarad | pF | 10⁻¹² |
| Femtofarad | fF | 10⁻¹⁵ |
Capacitance — Deep Technical Guide
What is capacitance?
Capacitance is the ability of a device or structure to store electric charge for a given voltage. It is a fundamental property used across electronics: smoothing supply rails, timing circuits, RF tuning, energy storage, sensors, and more. The basic relation is:
C = Q / V — where C is capacitance in farads (F), Q is charge in coulombs, and V is voltage in volts.
How capacitance arises (physical picture)
In a parallel-plate capacitor, capacitance depends on plate area (A), separation (d), and dielectric constant (ε):
C = ε × (A / d)
The dielectric material between plates increases capacitance by allowing more charge per volt. Real capacitors are variations on this geometry (rolled, stacked, surface-mount), and their capacitance depends on construction and dielectric properties.
Unit prefixes and why they matter
One farad is a very large capacitance in practical electronics. Most components are in microfarads (µF), nanofarads (nF), or picofarads (pF). Knowing prefixes avoids unit errors:
- 1 mF = 10⁻³ F
- 1 µF = 10⁻⁶ F
- 1 nF = 10⁻⁹ F
- 1 pF = 10⁻¹² F
- 1 fF = 10⁻¹⁵ F
Practical applications and typical values
Capacitors are everywhere. Typical examples:
- Decoupling near ICs: 10 nF – 100 nF (0.01–0.1 µF) ceramic capacitors.
- Bulk smoothing: 10 µF – 4700 µF electrolytic or polymer capacitors.
- RF tuning and filters: 1 pF – 100 pF (ceramic, NPO/COG for stability).
- Timing with RC networks: nF–µF range depending on R and target τ (tau) = R×C.
- Supercapacitors for energy storage: 0.1 F to several hundred F.
Measurement techniques
Common instruments:
- LCR meters: Measure inductance (L), capacitance (C), and resistance (R) precisely. Provide frequency-dependent values and dissipation factor (DF).
- Multimeters with capacitance range: Good for rough checks but limited for very small or very large values.
- Bridges and impedance analyzers: For lab-grade accuracy and frequency response.
- Time-constant method: Use an RC charging/discharging time constant to derive C when precise instrumentation is unavailable.
Real-component behaviors (non-ideal effects)
Real capacitors include parasitics: equivalent series resistance (ESR), equivalent series inductance (ESL), leakage resistance, and dielectric absorption. These affect performance at high frequencies, under DC bias, or when precise timing is required. Choose dielectric types (e.g., NPO/COG, X7R, Y5V) based on stability, temperature coefficient, and capacitance density.
Temperature, voltage, and frequency dependence
Dielectric materials can change capacitance with temperature and applied voltage (voltage coefficient). Ceramic types like X7R and Y5V are more temperature-dependent than C0G/NPO. For RF applications choose low-loss, stable dielectrics and account for ESL at high frequency.
Design formulas & examples
RC time constant: τ = R × C. Example: R=10 kΩ, C=10 nF → τ = 10,000 × 10×10⁻⁹ = 0.0001 s (100 µs).
Reactance: Xc = 1 / (2π f C). At 1 MHz, a 100 pF capacitor has Xc ≈ 1.59 kΩ.
Choosing capacitors (practical tips)
- For decoupling use a mix of values (e.g., 100 nF + 10 µF) to cover a broader frequency range.
- Check voltage rating: working voltage should be below the capacitor's rated voltage. For electrolytics, derate by 20–50% for reliability.
- For precision timing or filters, use NP0/C0G ceramics or film capacitors for low drift.
- Account for ESR in power circuits; low-ESR capacitors reduce heating and ripple.
Common mistakes and unit traps
- Mixing µF and nF: 1 µF = 1000 nF.
- Ignoring tolerance: capacitors can be ±1% to ±20% or more.
- Using polarized capacitors (electrolytics) in circuits where polarity can reverse.
Worked conversion examples
Example: Convert 220 nF to µF → 220 × 10⁻⁹ / 10⁻⁶ = 0.22 µF.
Example: 0.047 µF to pF → 0.047 × 10⁻⁶ / 10⁻¹² = 47,000 pF.
Extended FAQ (30+ practical questions)
What unit is best for PCB component labels?
Often µF for bulk values and nF/pF for small values; many manufacturers use µF (u), nF (n), pF (p) abbreviations.
How to interpret "104" on a ceramic capacitor?
“104” means 10 × 10⁴ pF = 100,000 pF = 100 nF.
Is 0.1u the same as 100n?
Yes — 0.1 µF = 100 nF.
Why do some capacitors have huge tolerances?
Cost and dielectric type; ceramic Y5V has high capacitance but poor tolerance and stability. Choose X7R/C0G for better performance.
What is ESR and why it matters?
Equivalent series resistance causes heat and reduces effectiveness at high ripple currents. Lower ESR is better for power applications.
Can I put capacitors in series or parallel?
Yes. Parallel adds capacitance (C_total = C1 + C2). Series reduces total (1/C_total = 1/C1 + 1/C2).
How do I measure small pF values accurately?
Use a precision LCR meter, guard connections, and short leads to minimize stray capacitance.
Why do RF circuits use tiny pF capacitors?
Because the reactance at RF frequencies requires very small capacitance values to achieve the desired impedance.
What's the effect of temperature on ceramic capacitors?
It depends on dielectric: C0G ≈ stable, X7R moderate drift, Y5V large drift.
Can capacitance change with DC bias?
Yes — many high-K ceramics show capacitance reduction under DC bias; account for this in designs.
How is a supercapacitor different from an electrolytic?
Supercapacitors store much more energy (farads vs microfarads) using electrochemical double-layer mechanisms; they have different voltage characteristics and are for energy storage, not bypassing noise at high frequency.
What is dielectric absorption?
Residual charge that slowly releases after discharge, affecting precision timing; film capacitors have lower dielectric absorption than electrolytics or ceramics.
Why do datasheets list frequency for capacitance?
Measured capacitance and loss can vary with frequency; datasheets show performance across frequencies.
When should I use an MLCC vs film capacitor?
MLCCs (ceramic) are compact and high-C, good for decoupling. Film caps are better for stability, low loss, and precision timing.
How to derate capacitors for reliability?
Use higher voltage ratings, avoid operating close to max temperature, and select capacitors with proven lifetime specs.
Can I replace a capacitor with a different dielectric?
Yes if the electrical characteristics (C, voltage, ESR, tolerance, tempco) remain acceptable for the circuit.
Why is a capacitor marked 0.047µF, not 47nF?
Both are valid; marking convention depends on manufacturer and region — they are equivalent (0.047 µF = 47 nF).
What is the typical tolerance for ceramic capacitors?
From ±0.1% (C0G) to ±20% (Y5V). Check part datasheets.
Do electrolytic capacitors have polarity?
Yes — they are polarized and must not be reverse-biased.
How do I reduce noise with capacitors?
Place decoupling caps close to IC power pins and use a combination of values to cover different frequencies.
What is 'self-resonant frequency'?
The frequency where capacitance and ESL resonate; above this the capacitor behaves inductively.
How to choose capacitors for audio circuits?
Use low-ESR, low-dielectric-absorption types (film capacitors) for coupling and timing in high-fidelity audio.
Why are MLCCs failing in some designs?
Cracking from mechanical stress, high DC bias reducing effective C, or insufficient voltage rating can cause failures.
What is "voltage coefficient"?
Change in capacitance with applied DC voltage; important for high-K ceramics.
Are polarized capacitors allowed in AC circuits?
No — polarized types (electrolytics) must not be used where polarity reverses unless specifically rated for AC.
How to measure leakage current?
Apply rated voltage and measure steady-state current with a picoammeter; leakage varies by dielectric and age.
What is "class 1" vs "class 2" dielectric?
Class 1 (e.g., C0G) = stable, low loss. Class 2 (e.g., X7R) = higher capacitance but more temp/frequency dependence.
Why is capacitance sometimes given at 1 kHz and sometimes at 100 kHz?
Different test conditions — check datasheet. Frequency affects measured capacitance and loss.
Can humidity permanently change capacitance?
Surface contamination and moisture can create leakage paths; proper coating and cleaning mitigate this.
Closing notes
Understanding capacitance, its units, and how real capacitors behave will help you pick the right part and avoid common mistakes. Use the converter above for quick unit changes, and consult datasheets for device-specific behaviors like ESR, temperature coefficient, and voltage dependence.