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electronics May 7, 2026 ◯ 10 min read

Capacitors Complete Guide: Types, Values, Codes, ESR, and How to Choose

by @jam3yy

What Is a Capacitor?

A capacitor is a passive electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by an insulating material called a dielectric. Capacitors block direct current (DC) while allowing alternating current (AC) to pass, making them essential for filtering, coupling, decoupling, timing, energy storage, and power conditioning. The fundamental relationship is C = Q/V, where capacitance (C) equals stored charge (Q) divided by voltage (V). Capacitance is measured in Farads (F), with most practical values ranging from picofarads (pF) to millifarads (mF).

Capacitor Fundamentals

Key Equations

FormulaSolves ForExample C = Q ÷ VCapacitance from charge and voltage1 coulomb at 10V = 0.1F Q = C × VStored charge100μF at 12V stores 1.2mC E = ½ × C × V²Stored energy in joules1000μF at 50V = 1.25 joules XC = 1 ÷ (2πfC)Capacitive reactance (AC resistance)10μF at 60Hz: XC = 1÷(2π×60×0.00001) = 265Ω τ = R × CRC time constant10kΩ + 100μF: τ = 1 second I = C × (dV/dt)Current through capacitor1μF with 1V/μs change: I = 1A

Capacitors in Series

1/Ctotal = 1/C1 + 1/C2 + 1/C3 + ...

Two equal capacitors in series: Ctotal = C/2. Voltage rating adds: two 100μF/25V caps in series = 50μF/50V.

Capacitors in Parallel

Ctotal = C1 + C2 + C3 + ...

Voltage rating stays the same (use the lowest rated cap's voltage).

Reading Capacitor Values

Electrolytic Capacitors (Large Cylindrical)

Values printed directly on the body. Example: "100μF 25V" = 100 microfarads, 25 volts maximum. The negative lead is marked with a stripe and minus signs. The positive lead is usually longer.

Ceramic Disc Capacitors (3-Digit Code)

CodeValue 10210 × 100 = 1000pF = 1nF 10310 × 1000 = 10,000pF = 10nF = 0.01μF 10410 × 10,000 = 100,000pF = 100nF = 0.1μF 10510 × 100,000 = 1,000,000pF = 1μF 22122 × 10 = 220pF 22222 × 100 = 2.2nF 47247 × 100 = 4.7nF 47347 × 1000 = 47nF 47447 × 10,000 = 470nF

Units: 3-digit codes are always in picofarads (pF). Letters after the code indicate tolerance: J=±5%, K=±10%, M=±20%. Voltage rating is often printed separately.

MLCC SMD Capacitors (Ceramic Chip)

CodeValue 1051μF 10610μF 2252.2μF 47647μF 107100μF 4754.7μF

Same 3-digit system but values tend to be larger. Some use explicit μF markings.

Tantalum Capacitors

Values printed directly: "106" = 10μF, "475" = 4.7μF. Voltage indicated by color or explicit marking. Stripe indicates positive terminal (opposite of electrolytics).

Film Capacitors

Values often in μF with explicit markings: "0.1μF 100V" or "100nJ100" (100nF, ±5%, 100V). The J indicates ±5% tolerance.

Capacitor Types Compared

1. Ceramic Capacitors (MLCC)

PropertyValue Capacitance range0.5pF to 100μF (typical: up to 10μF) Voltage rating6.3V to 500V+ Polarized?No — non-polarized ESRVery low (2-20mΩ typical) Price$0.01-0.50

Best for: High-frequency decoupling, filtering, timing, coupling. Use 100nF (0.1μF) ceramic caps next to every IC power pin — the most common capacitor application in digital circuits.

Dielectric types: C0G/NP0 (best stability, low capacitance), X7R (good general purpose), Y5V (high capacitance, poor stability — avoid for precision).

2. Aluminum Electrolytic Capacitors

PropertyValue Capacitance range0.1μF to 1,000,000μF (1F) Voltage rating6.3V to 450V+ Polarized?Yes — polarity must be observed ESRModerate to high (0.01Ω to 10Ω) Price$0.10-5.00

Best for: Power supply filtering, bulk energy storage, audio coupling, motor starting. Cheap high capacitance per volume.

Lifespan concern: Electrolytics dry out over time. Rated for 1,000-10,000 hours at rated temperature. Rule of thumb: every 10°C below rated temperature doubles life. A 105°C cap running at 45°C can last 15+ years. A 85°C cap running at 65°C might only last 3-5 years.

3. Tantalum Capacitors

PropertyValue Capacitance range0.1μF to 1000μF (typical: up to 220μF) Voltage rating2.5V to 50V Polarized?Yes — observe polarity ESRLow (0.05Ω to 2Ω) Price$0.30-5.00

Best for: Compact designs needing stable capacitance, military/aerospace (high reliability grades available). Excellent volumetric efficiency (more capacitance per cubic mm than aluminum electrolytic).

Warning: Tantalums can fail short-circuit violently if reverse voltage is applied or if voltage surge exceeds rating. Use a current-limiting resistor in series during power-up. Never exceed rated voltage — derate to 50% for reliability.

4. Polymer Aluminum Capacitors

PropertyValue Capacitance range2.2μF to 2700μF Voltage rating2V to 125V Polarized?Yes ESRVery low (3-50mΩ) Price$0.50-5.00

Best for: Switching power supplies, high-ripple-current applications, VRMs on motherboards. Replaces tantalum in many applications with better safety characteristics. Much lower ESR than traditional electrolytics.

5. Film Capacitors (Polyester/Mylar, Polypropylene, Polystyrene)

PropertyValue Capacitance range100pF to 100μF Voltage rating50V to 2000V+ Polarized?No — non-polarized ESRVery low Price$0.20-10.00

Best for: Audio circuits (excellent sound quality), high-voltage applications, motor run capacitors, precision timing, snubber circuits. Self-healing dielectric (small shorts burn clear rather than failing catastrophically).

6. Mica Capacitors

PropertyValue Capacitance range0.5pF to 10,000pF (10nF) Voltage rating100V to 1000V+ Polarized?No

Best for: RF circuits, high-frequency applications requiring extreme stability. Excellent temperature coefficient. Expensive and relatively large.

7. Supercapacitors (EDLC / Ultracapacitors)

PropertyValue Capacitance range0.1F to 3000F+ Voltage rating2.3V to 3.0V per cell (series for higher voltage) Polarized?Yes ESRLow to moderate (10mΩ to 100Ω depending on size) Price$1.00-50.00+

Best for: Energy storage, backup power, regenerative braking, burst power. NOT for filtering — high leakage current. Series connection requires active balancing circuits (unlike regular capacitors).

Capacitor Comparison Summary

TypeCap RangeVoltageESRPolarized?Best Use Ceramic (C0G/NP0)0.5pF-10nFHighUltra lowNoRF, precision timing, oscillators Ceramic (X7R)100pF-10μFHighVery lowNoDecoupling, general purpose, coupling Ceramic (Y5V)1nF-100μFMediumLowNoBulk decoupling (price sensitive) Aluminum Electrolytic0.1μF-1FMediumModerateYesPower filtering, bulk storage, audio Polymer Aluminum2.2μF-2700μFLow-MedVery lowYesSwitching supplies, VRMs, high ripple Tantalum0.1μF-1mFLowLowYesCompact, stable, high reliability Film (polypropylene)100pF-100μFHighVery lowNoAudio, high voltage, motor run Mica0.5pF-10nFHighUltra lowNoRF, precision, high frequency Supercapacitor0.1F-3000F2.5-3VLow-MedYesEnergy storage, backup power

Common Capacitor Applications

1. Power Supply Decoupling / Bypass

Place a 100nF (0.1μF) ceramic capacitor as close as physically possible to each IC power pin. This provides a local reservoir of charge for switching transients:

Placement rule: The capacitor lead/trace should be shorter than 10mm to the IC pin for effective high-frequency decoupling. Poor placement makes the capacitor useless above a few MHz.

2. Power Supply Filtering

After a rectifier, large electrolytic capacitors smooth the pulsating DC into steady DC:

C = Iload ÷ (2 × f × Vripple)

Example: 1A load, 60Hz mains, 1V ripple allowed: C = 1÷(2×60×1) = 8,333μF → use 10,000μF

3. Timing Circuits (RC Oscillators, 555 Timer)

555 astable frequency: f = 1.44 ÷ ((R1 + 2×R2) × C)

Example: R1=1kΩ, R2=10kΩ, C=10μF: f = 1.44÷((1000+20000)×0.00001) = 6.86 Hz

4. Audio Coupling

A capacitor blocks DC while passing audio AC signals:

C = 1 ÷ (2π × f × R) where f is lowest frequency and R is input impedance

Example: Coupling to a 10kΩ input, lowest frequency 20Hz: C = 1÷(2π×20×10000) = 0.8μF → use 1μF or 2.2μF

Cap choice: Film capacitors (polypropylene, polyester) are preferred for audio coupling due to low distortion. Electrolytics are acceptable for budget designs but introduce slight distortion.

5. Audio Filters (Crossover Networks)

Capacitors in series with speakers block low frequencies (high-pass filter). Capacitors in parallel shunt high frequencies to ground (low-pass filter when combined with inductors).

Example: 8Ω tweeter with 3kHz crossover: C = 1÷(2π×3000×8) = 6.6μF → use 6.8μF film capacitor

6. Motor Starting / Run Capacitors

AC induction motors need a phase shift to start:

Safety: Motor capacitors store lethal voltages. Always discharge with a 10kΩ 5W resistor before handling.

7. Snubber Circuits

A resistor-capacitor network absorbs voltage spikes from inductive loads (relays, motors, transformers):

8. Switching Regulator Input/Output

Switching regulators (buck, boost, buck-boost) need specific capacitors:

ESR: Equivalent Series Resistance

ESR is the internal resistance of a capacitor. It's the single most important parameter for power applications:

Why ESR Matters

ESR by Capacitor Type

TypeTypical ESR Ceramic X7R2-20mΩ Polymer aluminum3-50mΩ Tantalum50mΩ-2Ω Aluminum electrolytic (general)0.1Ω-10Ω Aluminum electrolytic (low ESR)10-500mΩ Film5-50mΩ

Measuring ESR

Capacitor Markings and Packages

SMD Ceramic Capacitor Packages

PackageDimensionsMax Cap (X7R)Common Use 02010.6mm × 0.3mm10nF/16VMobile devices, ultra-compact 04021.0mm × 0.5mm100nF/16VHigh-density designs 06031.6mm × 0.8mm1μF/16V or 100nF/50VDefault choice for most SMD decoupling 08052.0mm × 1.25mm4.7μF/16V or 1μF/50VHigher value, still easy to solder 12063.2mm × 1.6mm10μF/16V or 4.7μF/50VPower decoupling, larger values 12103.2mm × 2.5mm22μF/16VPower input filtering 18124.5mm × 3.2mm100μF/6.3VBulk decoupling

Electrolytic Capacitor Markings

Example marking: "1000μF 25V 105°C"

Tantalum Capacitor Case Sizes

Case CodeDimensions (L×W×H) A (3216)3.2mm × 1.6mm × 1.6mm B (3528)3.5mm × 2.8mm × 1.9mm C (6032)6.0mm × 3.2mm × 2.5mm D (7343)7.3mm × 4.3mm × 2.8mm E (7343-43)7.3mm × 4.3mm × 4.1mm

Capacitor Safety

Working Voltage Derating

Never operate a capacitor at its maximum rated voltage. Derating improves reliability:

Discharging Capacitors

Capacitors store energy and can deliver dangerous shocks:

Capacitor Failure Modes

TypeCommon FailureCause ElectrolyticDried out (high ESR, low capacitance)Age, heat, overvoltage ElectrolyticVented/burst (top domes or explodes)Overvoltage, reverse voltage, extreme ripple TantalumShort circuit (can catch fire)Overvoltage, reverse voltage, surge current CeramicMechanical crackBoard flex, impact, thermal shock CeramicMicrophonic (acts as microphone)Class 2 dielectrics (X7R, Y5V) — normal behavior FilmSelf-healing puncturesOvervoltage transients (usually recovers)

How to Test Capacitors

With a Multimeter (Basic)

  1. Set to capacitance mode (many multimeters have this)
  2. Discharge the capacitor first
  3. Connect leads (observe polarity for electrolytics)
  4. Reading should be within tolerance of marked value
  5. For electrolytics: also check with resistance mode — should show charging (resistance rises from low to high)

With an ESR Meter

  1. Can test in-circuit (desoldering not required if parallel resistance is high)
  2. Compare reading to known good values or manufacturer specs
  3. ESR over 2× the rated value indicates end of life

Visual Inspection

Where to Buy

Troubleshooting Capacitor Problems

SymptomLikely Cause Power supply hum/noiseHigh ESR in filter capacitors — replace with low-ESR types Voltage regulator oscillatingWrong type or too-small output capacitor — check datasheet requirements Amplifier hum/buzzFailed coupling capacitor (shorted or leaky) or inadequate power supply filtering Circuit works then diesTantalum shorted; electrolytic vented from overvoltage or heat Microcontroller resets intermittentlyMissing or inadequate decoupling capacitors on power pins High-frequency noise in analog circuitMissing bypass capacitors or wrong type (electrolytic instead of ceramic) Timer circuit runs fast or slowCapacitor tolerance or temperature coefficient; NP0/C0G for precision Switching supply overheatingOutput capacitors with too-high ESR — upgrade to polymer or ceramics