A standard ceramic capacitor marking like 104 translates to 10 followed by 4 zeros in picofarads (100,000 pF, which equals 100 nF or 0.1 µF). For electrolytics, the value is printed directly (e.g., 470µF 25V). If you are staring at a faded, unmarked, or vintage component, use the reference tables and decision paths below to identify it safely.

Safety First: Always discharge capacitors with a proper bleeder resistor (e.g., 10kΩ 5W) before handling. Electrolytics in power supplies can hold lethal charges for days after unplugging. Never short them directly with a screwdriver.

The Master Capacitor Marking Reference Table

The global standard for ceramic and film capacitor markings is the EIA (Electronic Industries Alliance) 3-digit code. The first two digits are the significant figures, and the third digit is the multiplier (number of zeros to add), yielding a base value in picofarads (pF).

Table 1: EIA 3-Digit Multiplier Codes (Base Value in pF)
3rd Digit Multiplier Example Code Calculation Final Value
0x122022 x 122 pF
1x1010110 x 10100 pF
2x10010210 x 1001,000 pF (1 nF)
3x1,00010310 x 1,00010,000 pF (10 nF)
4x10,00010410 x 10,000100,000 pF (100 nF / 0.1 µF)
5x100,00010510 x 100,0001,000,000 pF (1 µF)
8x0.0110810 x 0.010.1 pF (Specialty RF)
9x0.110910 x 0.11.0 pF (Specialty RF)

Following the numeric code, you will often see a single letter indicating tolerance. According to Electronics Tutorials, these letters map directly to standard manufacturing bins:

Table 2: Capacitor Tolerance Letter Codes
LetterToleranceCommon Application
J±5%Timing circuits, audio crossovers
K±10%General purpose filtering, decoupling
M±20%Bulk power supply smoothing
Z+80% / -20%Vintage noise suppression (Y-caps)

Rows and Symbols People Get Wrong

Even experienced bench technicians misread specific capacitor markings. Here are the most common traps and how to avoid them:

  • The "100" Trap: A marking of 100 does not mean 100 pF. It means 10 (significant digits) x 10^0 (multiplier). Therefore, 100 = 10 pF. If you need 100 pF, the correct code is 101.
  • The "R" Decimal Point: On SMD tantalums or larger film caps, you will see markings like 4R7 or R47. The "R" acts as a decimal point for microfarads. 4R7 = 4.7 µF. R47 = 0.47 µF.
  • Hidden EIA Voltage Codes: Tiny dipped ceramics or SMD parts often have a letter-number prefix that indicates voltage, not date codes. For example, 1H 104 means 50V (1H), 100nF (104). 1E is 25V, 1V is 35V, and 0J is 6.3V. Always check the All About Circuits capacitor guide for the full EIA voltage letter matrix before substituting parts.
Bench Tip: If you are measuring a 104 (100nF) ceramic capacitor with a multimeter's capacitance function and it reads 85nF, don't throw it away. Standard Y5V dielectrics lose massive capacitance under DC bias. Measure it with an LCR meter at 1kHz with 0V bias to get the true rated value.

Regional and Standard Variants (EIA vs IEC vs Vintage)

While the EIA 3-digit code dominates the global market today, you will encounter different standards depending on the equipment's origin and age.

IEC (International Electrotechnical Commission) Standard

Common in European schematics and printed on modern film capacitors (like WIMA brand), the IEC standard uses the unit prefix as the decimal point to avoid smudging.
Example: 4n7 means 4.7 nF. µ47 means 0.47 µF. 2p2 means 2.2 pF.

Old UK / European 5-Band Color Codes

If you are repairing 1970s British audio amplifiers or vintage radios, you will find tubular ceramic or paper capacitors with 5 color bands, read exactly like resistor color codes but resulting in picofarads.
Example: Brown (1), Black (0), Yellow (x10,000), White (±10%), Red (500V). This equals 100,000 pF (100nF), 10% tolerance, 500V rating. These are obsolete; modern equivalents do not use this physical marking scheme.

Decision Path: Identifying Faded, Damaged, or Unmarked Capacitors

When ink rubs off, heat shrinks the sleeve, or a manufacturer leaves a part completely blank, guessing is not an option. Use this decision tree to arrive at a concrete replacement.

Table 3: Faded or Unmarked Capacitor Decision Tree
Symptom / Condition Diagnostic Step Concrete Action / Replacement Pick
Faded Electrolytic in a switching power supply (e.g., 12V rail) Desolder one leg. Measure ESR and capacitance. If ESR is high or cap is >20% down, it is dead. Replace with exact µF, but step up voltage to the next standard tier. Pick: Panasonic FR Series 1000µF 25V (Low ESR, 105°C rated).
Unmarked Ceramic Disc used for logic IC decoupling Clean with IPA. Read with LCR meter at 1kHz. If it reads between 80nF and 120nF, it is a standard bypass cap. Do not reuse the vintage part. Pick: 100nF 50V X7R MLCC (Leaded or 0805 SMD depending on board).
Vintage 5-Band Color Code on a tube amplifier coupling stage Calculate value using the pF color chart. Check for physical bulging or wax leakage. Paper/wax caps drift and leak DC. Replace with modern film. Pick: WIMA MKS or MKP Film Capacitor of the exact calculated value and 630V rating.
Blank SMD Tantalum (no markings visible on the tan body) Identify the circuit block. If on a 3.3V microcontroller VCC rail, it is likely bulk decoupling. Tantalums fail short and cause fires. Pick: Replace with a 22µF 10V X5R Ceramic MLCC (1206 package) for safer, lower-ESR decoupling.

Safe Replacement Rules When Markings Are Gone

When you cannot determine the exact original specifications, follow these non-negotiable rules to prevent catastrophic failure or circuit malfunction:

  1. Never Guess the Voltage Rating: If a ceramic cap is unmarked and you don't know the circuit voltage, default to 50V for standard logic/bypass applications, or 1kV if it bridges a mains isolation barrier (Y-capacitor). For electrolytics, always step up to the next standard voltage tier (e.g., if the rail is 18V, use a 25V or 35V cap, never a 16V cap).
  2. Match the Dielectric, Not Just the Value: A 100nF Z5U ceramic and a 100nF C0G/NP0 ceramic have the exact same marking (104), but wildly different temperature and voltage stability. For timing oscillators or RF filters, you must use C0G/NP0. For general power decoupling, X7R is the correct default.
  3. Beware of Polarity on "Non-Polarized" Replacements: If you are replacing a faded bipolar electrolytic (common in audio crossover networks or motor run circuits) with two standard polarized electrolytics back-to-back, ensure you series them correctly (negative-to-negative) and double the µF value, as series capacitance halves the total.

For deep-dive specifications on dielectric drift and ESR degradation curves, consult the Cornell Dubilier technical papers archive. Always verify your final replacement with an LCR meter before soldering it into a high-density board.