Capacitor codes: how to read value, tolerance and voltage (with full chart)

There is very little room on a capacitor, so the value is not written out in full but as a code: 104, 4n7, 223J, 2A473K. Once you know three or four rules, though, you can read them in seconds. This guide collects all of them, with a complete table at the end to keep at hand when you take a board apart or sort out your parts drawer.

The three-digit code (the most common)

This is the code on ceramic and polyester capacitors. The value is always in picofarads (pF):

• the first two digits are the significant figures;
• the third digit tells you how many zeros to add.

The 104 is the most used capacitor in electronics: you will find one next to almost every integrated circuit, as supply decoupling.

Three special cases:

• below 100 pF the value is often printed directly: 47 means 47 pF. In the three-digit code the same value is 470 (47 and no zeros), so it means 47 pF, not 470 pF: 470 pF is written 471;
• the letter R acts as a decimal point: 4R7 = 4.7 pF, 1R0 = 1 pF;
• a third digit of 9 means multiply by 0.1 and 8 by 0.01: 229 = 2.2 pF. Rare, but it exists.

The letter in place of the decimal point (European code)

In the European system (IEC 60062) the unit letter replaces the decimal point: p for picofarads, n for nanofarads, µ or u for microfarads. It is the hardest system to misread.

• 4n7 = 4.7 nF = 4,700 pF;
• n47 = 0.47 nF = 470 pF;
• 2p2 = 2.2 pF;
• u22 (or µ22) = 0.22 µF = 220 nF.

Older American parts use microfarads with a decimal point instead: .01 = 0.01 µF = 10 nF, .0047 = 4.7 nF. If a number starts with a point, it is in µF.

The letter after the number: tolerance

A letter right after the value tells you how far the real value can be from the nominal one. 104K is a 100 nF ±10%.

B, C and D are used for small values, where a percentage would make no sense. Z is typical of cheap ceramic decoupling capacitors: the value can be almost double, rarely less.

Rated voltage

On film capacitors and many SMD parts the voltage is given as a digit and a letter, often before the value: 2A473J = 100 V, 47 nF, ±5%.

The digit is the power of ten (0 = units, 1 = tens, 2 = hundreds) and the letter the significant figures: A = 1.0, C = 1.6, E = 2.5, G = 4.0, H = 5.0, J = 6.3. When there is no code, the voltage is often printed in full (100 V, 630 V) or, on ceramic discs, 50 V is assumed.

Ceramics: C0G, X7R, Y5V and why they are not the same

Two ceramic capacitors both marked “104” can behave very differently. What matters is the dielectric, given as a three-character code:

• C0G (or NP0): extremely stable, it hardly changes with temperature or voltage. Used for filters, oscillators and timing. Only available in small values.
• X7R, X5R: a good compromise for decoupling. The code reads like this: the first letter is the minimum temperature (X = −55 °C), the digit the maximum (5 = 85 °C, 7 = 125 °C), the last letter the maximum capacitance change (R = ±15%).
• Y5V, Z5U: high capacitance in a small package, but very unstable: capacitance can drop by 80% with temperature.

One effect surprises many people: in X5R and X7R ceramics the capacitance drops with the applied DC voltage. A 10 µF 6.3 V part in an 0603 package biased at 5 V can deliver less than half its nominal value. The datasheet has a “DC bias” graph: always check it when choosing a capacitor for a regulator.

Electrolytic and tantalum: watch the polarity

Aluminium electrolytics have the value printed in full (470 µF 25 V) and a stripe with a minus sign marking the negative lead; the longer lead is the positive one. On the SMD version, the coloured mark on top again shows the negative side.

SMD tantalum capacitors do the opposite: the band marks the positive terminal. It is one of the most common assembly mistakes, and a tantalum capacitor fitted backwards can fail spectacularly. The value uses the three-digit pF code (107 = 100 µF, 475 = 4.7 µF) and the voltage a single letter: G = 4 V, J = 6.3 V, A = 10 V, C = 16 V, D = 20 V, E = 25 V, V = 35 V, H = 50 V.

What if nothing is written on it?

SMD ceramic capacitors (0402, 0603, 0805) usually carry no marking at all: you get the value from the schematic, the bill of materials, or by measuring it. A multimeter with a capacitance range is fine for medium values; for small values and accurate measurements you need an LCR meter. Discharge an electrolytic before measuring it: a large charged capacitor can damage the instrument.

On old polyester capacitors with coloured stripes, the value reads like a resistor (black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9), in picofarads, starting from the top stripe.

Test yourself

• 223J 2A: 22 + three zeros = 22,000 pF = 22 nF, ±5%, 100 V.
• 4n7K 630: 4.7 nF, ±10%, 630 V.
• 151: 15 + one zero = 150 pF.
• .047: 0.047 µF = 47 nF (American notation).
• 226 C on a tantalum: 22 + six zeros pF = 22 µF, 16 V.
• 8R2: 8.2 pF.

Complete table of values

The E12 series values, the most common ones, with the three-digit code, the European code and the American notation in microfarads. Below 10 pF the three-digit code uses R as the decimal point.