Capacitor Codes Demystified — 3-Digit Ceramic Capacitor Guide

You're looking at a tiny yellow disc with "104" printed on it. Is that 104 picofarads? 104 microfarads? Neither — it's 100,000 pF, which is 100 nF, which is 0.1 µF. The most common decoupling capacitor in all of electronics, and the marking doesn't remotely resemble any of those numbers.

How the 3-digit code works

The system is identical to resistor codes: two significant digits plus a multiplier.

Value in pF = (first digit × 10 + second digit) × 10^(third digit)

Code	Calculation	Value	Common name
100	10 × 10⁰ = 10	10 pF	—
101	10 × 10¹ = 100	100 pF	—
102	10 × 10² = 1,000	1 nF (1,000 pF)	—
103	10 × 10³ = 10,000	10 nF (0.01 µF)	—
104	10 × 10⁴ = 100,000	100 nF (0.1 µF)	Decoupling cap
105	10 × 10⁵ = 1,000,000	1 µF	—
220	22 × 10⁰ = 22	22 pF	Crystal load cap
330	33 × 10⁰ = 33	33 pF	Crystal load cap
471	47 × 10¹ = 470	470 pF	—
472	47 × 10² = 4,700	4.7 nF	—
473	47 × 10³ = 47,000	47 nF	—
474	47 × 10⁴ = 470,000	470 nF (0.47 µF)	—

The capacitor code decoder converts any 3-digit code to pF, nF, and µF simultaneously. Type the code, get all three units.

The unit confusion

Capacitance has three commonly used units that overlap annoyingly:

• pF (picofarads) = 10⁻¹² F
• nF (nanofarads) = 10⁻⁹ F = 1,000 pF
• µF (microfarads) = 10⁻⁶ F = 1,000,000 pF

A "0.1 µF" capacitor is the same as "100 nF" is the same as "100,000 pF" is the same as code "104." Datasheets, schematics, and component markings use all three units interchangeably. You'll eventually memorize the common ones, but until then, having a converter is essential.

Tolerance letters

Some capacitors add a letter after the 3-digit code:

Letter	Tolerance
J	±5%
K	±10%
M	±20%
Z	+80% / −20%

So "104K" means 100 nF ±10%. For most hobby projects, tolerance doesn't matter much. For timing circuits and filters, it does.

Voltage ratings

Ceramic capacitors also have voltage ratings, sometimes printed as a second number or letter code. Common voltage ratings:

Marking	Voltage
50V, 25V, 16V	Printed directly
1H	50V
1E	25V
1A	10V

If there's no voltage marking, check the datasheet. Never assume — exceeding the voltage rating causes capacitor failure (sometimes explosively with electrolytic caps).

The capacitors you'll use most

100 nF (0.1 µF) — Code 104

The universal decoupling capacitor. Place one next to every IC's power pins. It absorbs high-frequency noise and prevents supply voltage dips during switching. If a digital circuit is acting strange, adding 104 caps is the first debugging step.

10 µF — Code 106

Bulk decoupling for power supply filtering. Often electrolytic (which has the value printed directly) but ceramic 10 µF caps are increasingly common in small packages.

22 pF — Code 220

Load capacitors for crystal oscillators. A 16 MHz crystal for an ATmega328 (Arduino Uno) needs two 22 pF caps.

1 nF (1,000 pF) — Code 102

Common in RC filters and debouncing circuits. Paired with a 10 kΩ resistor, you get a time constant of τ = RC = 10,000 × 0.000000001 = 10 µs. Use the RC time constant calculator to explore different combinations.

Ceramic vs. electrolytic vs. film

The 3-digit code system is primarily used on ceramic capacitors — the small disc or MLCC types. Other capacitor types:

• Electrolytic — cylindrical, polarized, value printed directly (e.g., "100µF 25V"). Used for bulk decoupling and power supply filtering. Always observe polarity.
• Film — box-shaped, value printed directly or with 3-digit code. Used for audio, timing, and high-precision applications.
• Tantalum — teardrop shaped, polarized, value printed directly. Low ESR, good for sensitive analog circuits.

Reading tips

Ceramic capacitor markings are tiny. A magnifying glass or phone camera zoom helps. The code is usually on one flat side. If you see numbers like "104Z" or "103K," the first three digits are the value code and the letter is tolerance.

Some ceramic capacitors have no marking at all — especially small MLCC types. If you can't read the value, measure it with a multimeter that has a capacitance function, or trace it back to the BOM/schematic.