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Capacitor Code Calculator

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A ceramic capacitor is too small to print its value on, so it carries a code instead: two significant digits and a multiplier, always in picofarads. That last part is the trap — 104 means 100,000 pF, which is 100 nF, which is 0.1 µF, and a schematic, a datasheet and a shop listing will each prefer a different one of those three. Type the marking in and this gives all three, plus what any tolerance letter and voltage code alongside it mean.

Three digits, optionally with a tolerance letter and a voltage code — 104, 223K, 4R7, 102J 2A

A capacitor's opposition to AC falls as frequency rises, which is usually why it is fitted.

Try:

How to use the capacitor code calculator

  1. 1Type the code exactly as printed on the part — 104, 223K, 4R7, 47, or a code with a voltage suffix such as 102J 2A.
  2. 2Press Decode.
  3. 3Read the capacitance in all three units; the working line explains which rule was applied to your marking.
  4. 4Check the tolerance row if a letter was present, and the voltage row if a voltage code was.
  5. 5Change the frequency selector to see the part's reactance where it will actually be used.

Examples

The most common decoupling capacitor there is

Input
104
Result
100 nF — 10 × 10⁴ pF = 100,000 pF = 0.1 µF

If a board has a hundred identical small capacitors scattered next to every chip, this is what they are.

A code with a tolerance letter

Input
223K
Result
22 nF ±10%, so anywhere from 19.8 nF to 24.2 nF

K is ten percent, not kilo — a genuine source of confusion, since the same letter means something else entirely on a resistor.

R notation on a small value

Input
4R7
Result
4.7 pF

The R stands in for the decimal point, a convention used because a printed dot can rub off or be mistaken for dirt.

About the capacitor code calculator

Three units for one component

The reason a capacitor's value arrives in three different units is historical rather than logical. Picofarads suit the small ceramics used in radio work and are the unit the printed code is defined in. Microfarads suit the electrolytics used for power smoothing, and were the working unit long before the smaller parts became common. Nanofarads sit between them and are widely used in European schematics while being comparatively rare in American ones.

The consequence is that the same physical part is described as 100,000 pF, 100 nF or 0.1 µF depending on who is speaking, and none of them is wrong. Conversion is straightforward — a thousand picofarads make a nanofarad, and a thousand nanofarads make a microfarad — but doing it in your head while reading a marking off a part under a lamp is exactly where mistakes get made. This page does all three at once for that reason.

A fourth convention appears on schematics rather than parts: a bare decimal such as .1 usually means microfarads, and a bare integer usually means picofarads. It is a convention rather than a standard, and it is why a value on a drawing is worth checking against the parts list rather than trusted alone.

Why reactance is usually the number you actually want

A capacitor's opposition to alternating current falls as frequency rises, following Xc = 1/(2πfC). That single relationship explains most of what capacitors are used for, and it is why the same 100 nF part behaves so differently in different parts of a circuit.

At mains frequency that capacitor presents around 32 kΩ, which is effectively an open circuit — nothing useful passes. At 1 kHz it is 1.6 kΩ. At 1 MHz it is 1.6 Ω, low enough to be a short circuit for practical purposes. This is precisely the property that makes it a decoupling capacitor: it ignores the DC supply it sits across, while shorting the high-frequency noise on that supply straight to ground.

The same maths run backwards explains coupling capacitors, which pass a signal while blocking a DC offset, and it sets the corner frequency of every RC filter. The frequency selector on this page exists so the value can be read in the terms the circuit will actually experience, rather than as an abstract number of farads.

Frequently asked questions

Why is 104 not 104 picofarads?
Because the third digit is an exponent rather than a digit of the value. The marking works like scientific notation compressed into three characters: take the first two digits as a number, then append that many zeros. So 104 is 10 followed by four zeros, giving 100,000 pF. A genuine 104 pF part would be marked 101, which is 10 followed by one zero — and yes, that is exactly as confusing as it sounds until the rule is in front of you.
How do I tell a two-digit marking from a three-digit one?
Count the characters. A marking of one or two digits is the plain value in picofarads with no multiplier implied, so 47 is 47 pF. Three digits always means digit-digit-multiplier. The awkward case is 470, which is 47 followed by no zeros — also 47 pF — and it is why small-value capacitors are often marked with R notation instead, where 4R7 is unambiguous.
What does the letter after the number mean?
It is the tolerance, from the EIA series: J is ±5%, K is ±10%, M is ±20%, and F, G and H are the tighter 1%, 2% and 3% grades. Very small capacitors use B, C and D instead, which give an absolute tolerance in picofarads rather than a percentage, because a percentage of 2 pF would be meaningless. Z is the outlier at +80%/−20%, and it appears on cheap high-capacitance ceramics where the value is nominal at best.
What are X7R, C0G and Y5V?
They describe the dielectric, and they tell you how much the capacitance moves with temperature. C0G — often written NP0 — barely moves at all and is what timing and filter circuits need. X7R shifts by up to 15% across its range, which is fine for decoupling. Y5V is the one to watch: it can lose more than eighty percent of its marked capacitance at the extremes of its own rated temperature range, so a 10 µF Y5V part might behave like a 2 µF one on a cold morning.
Does the code tell me the voltage rating?
Only if a voltage code is printed alongside, and on small ceramics there often is not room. Where it appears it is usually a digit and a letter from the EIA table — 1H is 50 V, 2A is 100 V, 1J is 63 V. Some parts print the voltage in plain figures instead. Where nothing is marked, the rating has to come from the reel, the bag or the supplier's listing, and guessing it is a bad idea: exceeding the rating on a ceramic capacitor tends to short it rather than open it.

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