What the Capacitor Code Calculator does
This calculator decodes the markings on ceramic and film capacitors: the three-digit picofarad code, the tolerance letter, the voltage code and the dielectric class such as X7R or C0G. It gives the value in picofarads, nanofarads and microfarads at once, works out the reactance at a frequency you choose, and explains what the dielectric code means for the capacitance you will actually get.
The three-digit code follows the same logic as a resistor's: two significant digits and a power of ten - but counted in picofarads, which is why 104 is 100 nF and not 104 of anything.
How to use it
- Type the whole marking, including any letters. 104K1H is a complete marking: value, tolerance and voltage.
- If the dielectric is printed separately, or you know it from the part number, pick it from the list.
- Read the value in all three units. Which one you use is a habit rather than a rule - the same part is 100,000 pF, 100 nF and 0.1 uF.
- Enter a frequency to see the reactance. That is the number that tells you whether a decoupling or coupling capacitor is big enough.
- To work backwards, type a capacitance in the value box; the three-digit code appears in the code box.
Reading the results
Tolerance letters are a manufacturing window on the measured value at the standard test conditions, not a promise about behaviour in your circuit. On a Class 2 ceramic the DC bias effect is far larger than the tolerance.
The temperature range and change figure for a Class 2 dielectric - X7R's +/-15% from -55 to +125 C, for example - is the capacitance change allowed over that range with no DC applied. Apply rated voltage and a small X7R part can lose half its capacitance on top of that.
A voltage code is a maximum, not an operating point. Class 2 ceramics lose capacitance steadily as the applied DC approaches the rating, so a 16 V part run at 12 V is a poor choice even though it is within specification.
Worked example: a disc marked 104K1H
104 is the value in picofarads: 10 followed by four zeros, so 100,000 pF. That is 100 nF, or 0.1 uF - the workhorse decoupling capacitor.
K is the tolerance letter for +/-10%, so the part measures between 90 and 110 nF at the standard test conditions. 1H is the EIA voltage code for 50 V.
At 1 kHz its reactance is 1 / (2 pi x 1000 x 1e-7) = 1,592 ohms; at 100 kHz it is 15.9 ohms. That fall with frequency is the whole point of a decoupling capacitor - and why its real limit is the inductance of the package and the via, not the capacitance, once you get into the tens of megahertz.
Formulas and scoring rules
- Three-digit code
C[pF] = (first two digits) x 10^(third digit)104 = 10 x 10^4 = 100,000 pF. A third digit of 8 means x0.01 and 9 means x0.1, so 229 is 2.2 pF.- Unit conversion
1 uF = 1,000 nF = 1,000,000 pF- Capacitive reactance
Xc = 1 / (2 pi f C)In ohms, with C in farads. It halves every time the frequency doubles.- Tolerance letters
B +/-0.1 pF, C +/-0.25 pF, D +/-0.5 pF, F +/-1%, G +/-2%, J +/-5%, K +/-10%, M +/-20%, Z +80/-20%- EIA dielectric code
first letter = low temperature, digit = high temperature, last letter = capacitance changeX = -55 C, Y = -30 C, Z = +10 C; 5 = +85 C, 6 = +105 C, 7 = +125 C; R = +/-15%, S = +/-22%, V = +22/-82%.
Class 1 and Class 2 ceramics are different components
C0G (also sold as NP0) is a Class 1 dielectric: its capacitance is stable to about 30 ppm/K, it does not age, it does not lose value under DC bias and it is not microphonic. It is also bulky and expensive, so it is found where the value matters - filters, timing, oscillators.
X7R, X5R, Y5V and the rest are Class 2: high permittivity ceramics that pack far more capacitance into the same package, at the cost of temperature drift, ageing of a few per cent per decade-hour, piezoelectric noise and a large loss of capacitance under DC bias. They are excellent decoupling capacitors and poor timing capacitors, and swapping one for the other is a real circuit change, not a substitution.
The DC bias effect, which no marking tells you about
Apply DC to a Class 2 ceramic and its capacitance falls. How far depends on the dielectric, the case size and the voltage rating: a 10 uF X5R in an 0805 case at its rated 6.3 V can measure 2 uF or less. Nothing in the 106K marking hints at this, and a meter with no bias applied will read the full value.
The practical rules are to derate hard - choose a rating two or three times the working voltage - to prefer a larger case size for the same value, and to read the manufacturer's bias curve for the exact part rather than assuming. For anything where the value has to be right, use a Class 1 or film capacitor instead.
Limitations: what the result does not prove
- Voltage codes are decoded from the common EIA and JIS tables. Manufacturers do use other schemes, and the data sheet for the part is the authority.
- Electrolytic and tantalum capacitors are usually marked with the value and voltage printed plainly rather than in code, and they have polarity, ripple-current and lifetime ratings this page says nothing about.
- The calculator reads the marking. It cannot tell you the capacitance under DC bias, the ESR, the self-resonant frequency or the ageing state of the part - all of which can matter more than the printed value.
- A tolerance letter applies at the manufacturer's test conditions, typically 1 kHz and 1 V RMS with no DC. Your circuit is unlikely to match those.
Privacy: where your data goes
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Standards and sources
- IEC 60062 - Marking codes for resistors and capacitors - checked 19 Sep 2026
- Murata - Basics of capacitors: temperature characteristics and DC bias
- KEMET - Ceramic capacitor dielectric classes and characteristics
Frequently asked questions
What value is a capacitor marked 104?
100 nF, which is also written 0.1 uF or 100,000 pF. The code is read in picofarads: 10 followed by four zeros. It is by far the most common decoupling value, which is why the marking is so familiar.
What does the letter after the number mean?
It is the tolerance. J is +/-5%, K is +/-10% and M is +/-20%; on small-value parts B, C and D give an absolute tolerance in picofarads instead. Z is the lopsided +80%/-20% used on cheap high-value ceramics.
What is the difference between X7R and C0G?
C0G is a Class 1 dielectric: stable with temperature and voltage, no ageing, no DC bias loss. X7R is Class 2: much more capacitance per package but +/-15% over temperature, a few per cent of ageing and a large loss of capacitance under DC bias. Use C0G where the value matters and X7R where bulk capacitance matters.
Why does my 10 uF ceramic measure much less in circuit?
DC bias. Class 2 ceramics lose capacitance as DC voltage is applied, and a small-package high-value part can lose most of it at its rated voltage. Choose a higher voltage rating, a bigger case, or a different dielectric - and read the manufacturer's bias curve.
What does a code like 1H or 2A on a capacitor mean?
It is the voltage rating in EIA code: 1H is 50 V, 1J is 63 V, 2A is 100 V and 2E is 250 V. The digit gives the decade and the letter the significant figure. The data sheet is definitive, since not every manufacturer uses the same table.
How do I read a capacitor marked 229 or 109?
An 8 or a 9 in the third position is a fractional multiplier, not a count of zeros: 8 means x0.01 and 9 means x0.1. So 229 is 22 x 0.1 = 2.2 pF and 109 is 1 pF. These appear on very small RF and timing capacitors.
Is 0.1 printed on a capacitor microfarads or picofarads?
Microfarads. A marking with a decimal point, typical of film and electrolytic parts, is read in microfarads, so 0.1 is 100 nF and 0.047 is 47 nF. Codes without a decimal point on ceramics are read in picofarads.
Does a higher voltage rating hurt anything?
Only size, cost and sometimes availability. Electrically a higher rating is better: on Class 2 ceramics it directly reduces the DC bias loss, and on electrolytics it usually brings a longer life at the same ripple current.
Last reviewed by the A2Z.Tools team against the sources listed above.
