How to read capacitor codes and markings
A resistor gets colour bands; a capacitor gets a cryptic print. 104 is 100 nF, 22 is 22 pF, 4n7 is 4.7 nF, 0.1 is 0.1 µF, and the letters after them say how accurate the part is and how much voltage it takes. This calculator reads any of those into a value with its tolerance window, voltage and dielectric, and turns a value you have into the code a part would carry.
How to use the capacitor code calculator
- Type the marking as printed: 104, 104K, 104K 2A, 22, 4n7, n47, 0.1, 100nF, 4.7u. Letters and codes after the digits are read too.
- Or type a value you calculated (100n, 4.7uF) and read off the three-digit code a part would carry.
- Fill in what the part did not print: the tolerance letter, the EIA voltage code and the ceramic dielectric, from the selects.
- The drawing shows the disc with each part of the marking called out; click a callout for its meaning. The panel gives the value in pF, nF and µF, the tolerance window and the decoder; the Common codes tab lists 100 to 106.
Three-digit codes
C = (first two digits) × 10(third digit) pF
The commonest marking on ceramic discs and chips. The first two digits are the significant figures, the third the number of zeros, and the unit is always picofarads: 101 = 100 pF, 102 = 1 nF, 103 = 10 nF, 104 = 100 nF, 105 = 1 µF, 106 = 10 µF. Two exceptions: a third digit of 8 means ×0.01 and 9 means ×0.1, so values under 10 pF can be written (229 = 2.2 pF). A marking of only one or two digits is the value in picofarads: 22 is 22 pF, 47 is 47 pF.
Other ways to write the value
Film capacitors and larger parts usually print the value. A bare decimal is microfarads (0.1 = 100 nF, .047 = 47 nF); a number with a prefix letter is what it says (100n, 4.7u, 10µF); the letter may stand in for the decimal point (4n7 = 4.7 nF, 2u2 = 2.2 µF) or for a leading "0." (n47 = 0.47 nF = 470 pF, p22 = 0.22 pF). Electrolytics print the value in µF with the voltage and a stripe for the negative lead. Tiny SMD ceramics are usually not marked at all; tantalum chips use a letter for the voltage and a stripe for the positive end.
Tolerance letters
| Letter | Tolerance | Where you see it |
|---|---|---|
| B · C · D | ±0.1 · ±0.25 · ±0.5 pF | Below 10 pF, where percent makes no sense |
| F · G | ±1% · ±2% | C0G/NP0 ceramics, precision film |
| J | ±5% | Film, better ceramics, timing parts |
| K | ±10% | Most film and X7R ceramics |
| M | ±20% | Discs, electrolytics, general decoupling |
| Z | +80% / −20% | Y5V and Z5U decoupling only |
Voltage codes
The EIA code is a digit for the decade and a letter for the mantissa: 0J 6.3 V, 1A 10 V, 1C 16 V, 1E 25 V, 1H 50 V, 1J 63 V, 2A 100 V, 2D 200 V, 2E 250 V, 2G 400 V, 2J 630 V, 3A 1 kV. Many parts print the voltage outright (50V, 250V~ for AC-rated). Run ceramics at half their rating or less: a class 2 ceramic at its full voltage may have lost half its capacitance, and a film capacitor lasts longer for every volt of margin.
Dielectrics
| Code | Class | Range and drift | Use |
|---|---|---|---|
| C0G | Class 1 | −55 to +125 °C, ±30 ppm/°C | Also NP0. Stable, precise, no drift with voltage; timing and RF |
| X7R | Class 2 | −55 to +125 °C, ±15% | General purpose; loses capacitance with DC bias and age |
| X5R | Class 2 | −55 to +85 °C, ±15% | Like X7R with a narrower range; most SMD decoupling |
| Y5V | Class 2 | −30 to +85 °C, +22/−82% | Cheap and unstable; decoupling only |
| Z5U | Class 2 | +10 to +85 °C, +22/−56% | Old general-purpose discs; avoid for anything that matters |
The code is three characters: the lowest temperature (X −55 °C, Y −30 °C, Z +10 °C), the highest (5 = 85 °C, 7 = 125 °C) and the change over that range (R ±15%, U +22/−56%, V +22/−82%). Class 1 parts (C0G/NP0) are a different kind of ceramic: small values, no voltage or ageing drift, ±30 ppm/°C.
Your marking, read out
- Value: 104 is 100 nF = 100,000 pF = 0.1 µF; the three-digit code is 104.
- Tolerance: K = ±10%, so 90 nF to 110 nF.
- Voltage and dielectric: 2A = 100 V.
- Typical use: decoupling and bypass, coupling, filters.
Worked example: 104K 2A
The figures are 10 and the multiplier 4: 10 × 10⁴ pF = 100,000 pF = 100 nF, the universal decoupling capacitor. K is ±10%, so the part is really between 90 nF and 110 nF. 2A is the EIA code for 100 V; on a 5 V rail that is plenty of margin. If it is an X7R chip it will also lose a few percent under 5 V of bias and a few more over the years, which for decoupling does not matter at all.
Questions
Is 104 the same as 0.1 and 100n?
Yes: 100 000 pF = 100 nF = 0.1 µF. Ceramics are coded, film parts print the value, engineers say all three.
What does a marking like 2A104K mean?
Some makers put the voltage code first: 2A (100 V), 104 (100 nF), K (±10%). The calculator accepts the parts in either order when they are separated by a space; type 104K 2A.
Why is my 100 nF capacitor measuring 70 nF?
Class 2 ceramics (X7R, Y5V) lose capacitance with DC bias, temperature and age, and a cheap meter measures at a low voltage and a frequency the part may not like. For a value that must hold, use C0G/NP0 or film.
Which end is which?
Ceramic and film capacitors have no polarity. Electrolytics mark the negative lead with a stripe (and it is shorter); tantalums mark the positive end.