Capacitor code decoder

A 100 nF capacitor is marked 104. The first two digits are the value and the third is the number of zeros, in picofarads. So 104 is 10 followed by four zeros: 100 000 pF, which is 100 nF or 0.1 µF. A letter after the digits is the tolerance — J is ±5 %, K is ±10 %, M is ±20 %. A prefix such as 2A is the rated voltage, here 100 V. Enter any marking below to decode it, or a value to get its code.

The decoder also reports reactance and stored energy at your frequency and voltage, and what the X7R and C0G classes actually promise.

Fig 1 — Marking "104" reads 100 nF.

Marking (104, 104K, 2A104K, 4n7, 0.1u)

Frequency for reactance (0 to skip) (Hz)

Voltage for stored energy (0 to skip) (V)

Capacitance: 100 nF (100,000 pF)
Reactance at 1.00 kHz: 1.59 kΩ
Energy at 3.3 V: 544 nJ

Dielectric	Range	ΔC over range	Notes
C0G / NP0	−55 to +125 °C	±0.54 % (0 ± 30 ppm/°C)	Class 1. No DC-bias loss, no ageing, no piezo noise. Use for timing, filters, oscillators.
X5R	−55 to +85 °C	±15 %	Class 2. Loses capacitance under DC bias; ages ~2.5 %/decade-hour.
X7R	−55 to +125 °C	±15 %	Class 2. The default for decoupling. Same DC-bias caveats as X5R.
X7S	−55 to +125 °C	±22 %	Class 2. Higher volumetric density than X7R, more bias loss.
Y5V	−30 to +85 °C	+22/−82 %	Class 2. Can lose most of its value hot or biased. Avoid in anything that matters.
Z5U	+10 to +85 °C	+22/−56 %	Class 2. Obsolete for new designs.

How this is calculated

Standard: IEC 60062 (marking codes); EIA-198 (ceramic classes, voltage codes)

$\text{dd}X \;\rightarrow\; \text{dd} \times 10^{X}\ \text{pF}$: Two significant digits and a decade. X = 8 and X = 9 are the exceptions: they mean × 0.01 and × 0.1.
$\text{J} = \pm 5\,\%, \quad \text{K} = \pm 10\,\%, \quad \text{M} = \pm 20\,\%, \quad \text{C} = \pm 0.25\ \text{pF}, \quad \text{D} = \pm 0.5\ \text{pF}$: Tolerance letter, the last character of the code. The full table runs beyond these five.
$\text{0J} = 6.3\ \text{V}, \quad \text{1A} = 10\ \text{V}, \quad \text{1C} = 16\ \text{V}, \quad \text{1E} = 25\ \text{V}, \quad \text{1H} = 50\ \text{V}, \quad \text{2A} = 100\ \text{V}$: EIA voltage prefix, two characters in front of the value: the digit is the decade and the letter the mantissa.
$X_C = \frac{1}{2\pi f C}$: Reactance at a frequency.
$E = \frac{1}{2} C V^2$: Energy stored at a voltage.

Assumptions

Codes are read as printed; a part with no code (most MLCCs) can only be identified from its reel or measured.
The dielectric table gives the EIA temperature characteristic only. DC-bias loss in class 2 parts is not in the code and can halve the capacitance; check the vendor curve.
Reactance is for an ideal capacitor. Above self-resonance the part is an inductor — see the decoupling tool.
Tantalum and electrolytic parts mark value and voltage in plain text and are polarised; the decoder does not know which package it is looking at.

What a capacitor code encodes

The marking on a capacitor is two significant digits and a multiplier, in picofarads. That is the whole scheme, and it is the reason this site is called 100nF: the most common capacitor on any board is printed 104.

104  →  10 × 10^4 pF  = 100 000 pF = 100 nF
221  →  22 × 10^1 pF  = 220 pF
479  →  47 × 0.1 pF   = 4.7 pF     multiplier 9 means ×0.1
158  →  15 × 0.01 pF  = 0.15 pF    multiplier 8 means ×0.01
47   →  47 pF                       one or two digits are pF directly

The decoder also takes the unit-letter forms used on film and larger parts, letter in place of the decimal point: 4n7 is 4.7 nF, 4R7 is 4.7 pF, 0.1u and 100nF are 100 nF. A trailing letter is the tolerance, as vendor and EIA marking tables print it: B ±0.1 pF, C ±0.25 pF, D ±0.5 pF (absolute, for small class 1 parts), F ±1 %, G ±2 %, H ±3 %, J ±5 %, K ±10 %, M ±20 %, N ±30 %, P +100/−0 % (the EIA "guaranteed minimum value" code), Z +80/−20 %. IEC 60062 uses the same letters with two differences worth knowing: its H is ±2.5 %, and it defines no P. A leading digit-letter pair is the EIA-198 voltage: digit is the decade, letter the mantissa, so 1H is 5.0 × 10 = 50 V, 2A is 100 V, 1E is 25 V, 1C is 16 V, 0J is 6.3 V.

Going the other way, the tool gives the three-digit code for a value if one exists (two significant digits, 10 pF to 990 µF), plus reactance at a frequency, stored energy at a voltage, and the dielectric table — the reactance and energy expressions under How this is calculated above.

Class 1 ceramics (C0G/NP0) are paraelectric: ±30 ppm/°C, no ageing, no voltage dependence, no piezo effect, but low permittivity, so they top out near 100 nF. Class 2 (X5R, X7R, X7S, Y5V, Z5U) are ferroelectric barium titanate: ten to a hundred times the capacitance per volume, and every fault below follows from that material. The code is EIA-198: X = −55 °C, 5 = +85 °C, 7 = +125 °C, R = ±15 %, S = ±22 %, V = +22/−82 %.

Capacitor code chart: the common values

Every code below is the same two-digits-and-a-multiplier rule applied to the E-series values that actually come on a reel. Read it either way: a part marked 104 is 100 nF, and a 100 nF part is marked 104. The third column is the same capacitance written the way other datasheets write it, because 100 nF, 0.1 µF and 100000 pF are one component. Spelled out, those units are picofarad, nanofarad and microfarad, and a code always resolves to picofarads before anything else.

Code	Capacitance	Also written
100	10 pF	—
220	22 pF	—
470	47 pF	—
101	100 pF	—
221	220 pF	—
471	470 pF	—
102	1 nF	0.001 µF, 1000 pF
222	2.2 nF	0.0022 µF, 2200 pF
472	4.7 nF	0.0047 µF, 4700 pF
103	10 nF	0.01 µF, 10000 pF
223	22 nF	0.022 µF, 22000 pF
473	47 nF	0.047 µF, 47000 pF
104	100 nF	0.1 µF, 100000 pF
224	220 nF	0.22 µF, 220000 pF
474	470 nF	0.47 µF, 470000 pF
105	1 µF	—
225	2.2 µF	—
475	4.7 µF	—
106	10 µF	—
226	22 µF	—
476	47 µF	—
107	100 µF	—

Below 10 pF the three-digit form runs out, because two significant digits and a multiplier cannot express 4.7 pF without the fractional multipliers 8 and 9: 479 is 47 × 0.1 pF = 4.7 pF, and 158 is 15 × 0.01 pF = 0.15 pF. Small parts are more often marked with the letter-for-decimal-point form instead, 4R7 for 4.7 pF, or simply 47 for 47 pF. A trailing letter is always the tolerance and never part of the number, so 681J is 680 pF at ±5 %, not 681 of anything.

Worked example: decoding 2A104K

A tantalum or large ceramic marked 2A104K.

2A     →  A = 1.0, decade 2      →  1.0 × 10^2 = 100 V
104    →  10 × 10^4 pF           →  100 nF
K      →  ±10 %

Xc at 1 kHz = 1 / (2π × 1000 × 100e-9)
            = 1 / 6.283e-4       = 1.59 kΩ

E at 3.3 V  = 0.5 × 100e-9 × 3.3²
            = 0.5 × 100e-9 × 10.89 = 545 nJ

Encoding back: 100 nF is 100 000 pF, 10 with four zeros, so 104; 4.7 nF is 4700 pF, so 472. A 3-digit code cannot express 4.75 nF and the tool says so.

Where the marked value stops being the real one

DC bias. The marked value of a class 2 part is measured at 1 kHz, 1 V RMS, no DC. Under bias the dielectric saturates and the capacitance falls, faster in small packages where the field per volt is higher. A 10 µF 0603 X5R rated 6.3 V holds around 40 % at 5 V; the same value in 0805 rated 10 V holds around 70 %. Do not guess: Murata SimSurfing and KEMET K-SIM publish per-part-number curves, and parts with the same label differ between vendors. The tool reports the number on the body; the number in the circuit is that times the bias factor.

Ageing. Class 2 ceramics lose capacitance logarithmically after their last trip above the Curie point, 1 to 2.5 % per decade-hour for X7R, more for X5R and Y5V. The marking is referenced to 1000 hours and reflow resets the clock, so a board read the day after assembly is higher than the same board a year later.

Piezoelectric noise. The same material makes a class 2 MLCC an actuator. Ripple makes it sing through the board; worse, flex or vibration produces a voltage across a coupling cap in an audio or sensor path. C0G, film or tantalum for signal chains that get shaken.

Tantalum. Moulded tantalums carry the value in µF and the voltage in digits, or the EIA code this tool decodes. The bar marks the positive end, opposite to an electrolytic. Reverse polarity or a spike ignites MnO2 tantalums, so derate to 50 % of rated voltage, 30 % on a battery input. Polymer tantalums fail short without burning and tolerate 80 to 90 %.

Film. Polyester and polypropylene use the unit-letter form (2n2, 100n, 0.1u) plus the voltage in digits. No bias effect, low loss, self-healing, which is why mains X and Y parts are film. Polyester drifts about +5 % over 0 to 85 °C; polypropylene does not.

Unmarked MLCCs. Nothing smaller than 1206 is marked. Value, dielectric and voltage exist on the reel label only; a loose 0402 is a 0402 of unknown value. Keep the reel, or put it on an LCR meter.

Common capacitor marking mistakes

Reading 104 as 104 pF. Three digits are never literal; two are.
Taking the marked 10 µF at face value on a 5 V rail. Check the DC-bias curve for that exact part number; the 0603 may be 4 µF in the circuit.
Reading the tantalum bar as the negative end.
Substituting Y5V or Z5U for X7R because the package matches. Y5V at 85 °C and rated voltage can be a tenth of its marked value.
Confusing the tolerance letter with the voltage code. 104K is ±10 %; the voltage is the digit-letter pair in front. M after the digits is ±20 %, not µ.
Using a class 2 cap for timing or a filter corner: ±15 % tempco, minus bias loss, minus ageing.