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 How to read Capacitor Codes
Large capacitors have the value printed plainly on them, such as 10.uF (Ten Micro Farads) but smaller disk types, along with plastic film types, often have just two or three numbers printed on them.
Most of those will have three numbers, but sometimes there are just two numbers. These are read as Pico-Farads. An example: 47 printed on a small disk can be assumed to be 47 Pico-Farads (or 47 puff as some like to say)
Now, what about the three numbers? It is somewhat similar to the Resistor Codes. The first two are the 1st and 2nd significant digits and the third is a multiplier code. Most of the time the last digit tells you how many zeros to write after the first two digits, but the standard (EIA standard RS-198) has a couple of curves that you probably will never see. But just to be complete here it is in a table.
What these numbers don't tell us is the ESR rating of a capacitor. Despite popular belief capacitors will often still have the correct value of capacitance when they fail. To truly check a capacitor's condition, you need a meter that measures ESR.
|Table 1 Digit multipliers|
|Third digit||Multiplier (this times the first two digits gives you the value in Pico-Farads)|
|6 not used|
|7 not used|
Now for an example: A capacitor marked 104 is 10 with 4 more zeros or 100,000pF which is otherwise referred to as a .1 uF capacitor.
Most kit builders don't need to go further, but I know you want to learn more. Anyway, Just to confuse you some more there is sometimes a tolerance code given by a single letter. These letters are in alphabetical order; the farther down in the alphabet, the lower the tolerance.
So a 103J is a 10,000 pF with +/-5% tolerance
|Table 2 Letter tolerance code|
|Letter symbol||Tolerance of capacitor|
 Dielectric Codes
There are two groups of EIA codes - Class-1 and class-2
Now to be really complicate things there is sometimes a letter-number-letter (like Z5U) code that gives information. Table 3 shows how to read these cryptic codes. A "224 Z5U" would be a 220,000 pF (or .22 uF) cap with a low temperature rating of +10 deg C a high temperature rating of +85 Deg C and a tolerance of +22%,-56%.
|Table 3 Dielectric codes|
| First symbol
| Low temperature
| Second symbol
| High Temperature
| Third Symbol
| MAX. Capacitance |
|X||-55 ° C||2||+45 ° C||A||+/- 1.0%|
|Y||-30 ° C||4||+65 ° C||B||+/- 1.5%|
|Z||+10 ° C||5||+85 ° C||C||+/- 2.2%|
|6||+105 ° C||D||+/- 3.3%|
|7||+125 ° C||E||+/- 4.7%|
|8||+150 ° C||F||+/- 7.5%|
The EIA three-character code for the material capacitance-temperature slope is derived from the low and high temperature limit, and the range of capacitance change. Cøg (C0g) or NPø (NP0) refer to caps that don't have any temperature drift (at least in theory <g> they all have SOME amount of drift - think
zero tempco = approximately +-30ppm) (Cog should be C-zero-g npo should be np-zero. The zero is for zero drift.)
| ppm/°C ppm
(ppm = Parts per million )
|Multiplier||Tolerance in ppm/°C (25-85 °C)|
|C: 0.0||0: -1||G: ±30|
|B: 0.3||1: -10||H: ±60|
|L: 0.8||2: -100||J: ±120|
|A: 0.9||3: -1000||K: ±250|
|M: 1.0||4: +1||L: ±500|
|P: 1.5||6: +10||M: ±1000|
|R: 2.2||7: +100||N: ±2500|
|S: 3.3||8: +1000|
The industry version uses either an 'N' or 'P' prefix for Negative, P for Positive) followed by the slope coefficient.
 Color codes
There are some Capacitor color codes - the last dot is the tolerance code where brown is +/-1% red +/-2% as in the resistor color code with two exceptions black is +/- 20% and white is +/- 10% going backward the three dots to the left of the tolerance dot form the value in pF There will be two or three more color dots before the value but they mean different things about temperature range and coefficient depend which one of three systems is used - so I will leave it out for now unless some one asks.
 EIA Part Number Codes
There are two more number systems seen on caps. The first one can be recognized as the EIA because it starts with an R.
R DM 15 F 471(R) J 5 O (C)
The above number means the following
|R||tells us this is an EIA code|
|DM||is a dipped case style CM would be a molded case style|
|15||is the case size code - if anyone asks I will put up a table for this|
|F||is the characteristic code from table 4|
|471R|| the R is a decimal point when used (not often) the|
first two digits form the significant value and the third
is the multiplier thus, this is a 470pF part
|J||is the capacitance tolerance code as given in table 2 above thus J is a 5% part|
|5||is the DC working voltage in hundreds of volts (EIA only) thus 500V|
|O||is the temperature range from table 5|
|C||tells us the leads are crimped where a S would tell us they are straight.|
 Military part number code
CM 15 B D 332 K N 3
|CM||is the case code - DM is a dipped case style CM would be a molded case style|
|15||is the case size code - if anyone asks I will put up a table for this|
|B||characteristic code tells us it doesn't have a drift specified (from table 4)|
|D||is the Military voltage code from table 6|
|332||tells us that it is 3,300pF|
|K||tells us from table 2 that this is a 10% part|
|N||gives us our temperature range of -55 to 85°C from table 5|
|3||The 3gives the vibration grade 3 tells us 20g at 10 to 2,000 hz for 12 hours (1 is 10G at 10 to 55 Hz for 4.5 hours)|
|Table 4 characteristic codes|
| EIA or MIL
| Maximum range of |
|B||Not specified||Not specified|
|C||+/-(0.5% + 0.1pF)||+/- 200 ppm/°C|
|D||+/-(0.3% + 0.1pF)||+/- 100 ppm/°C|
|E||+/-(0.1% + 0.1pF)||-20 to +100 ppm/°C|
|F||+/-(0.05% + 0.1pF)||0 to +70 ppm/°C|
| Table 5 |
|M||-55 to 70 °C|
|N||-55 to 85 °C|
|O||-55 to 125 °C|
|P||-55 to 150 °C|
| Table 6 |
Mil voltage range
code in volts
 Ceramic caps may be tiny, but they have lots of non ideal qualities so calculating total tolerance can get ugly
There is a voltage dependency that is in addition to both the initial tolerance and the temperature coefficient. For some types, operating at full rated voltage reduces the capacitance to less than half of the zero voltage capacitance. Z5U types have a knee at about 10Vdc and by 50Vdc they are at 50% of their rated value! X7R types have a similar knee at about 20V .
The high K types also slowly lose capacitance over time, but can be reset back to full value by heating them above their Curie temperature (125 - 150 degC for a couple of hours). Cøg types are stable over time, but X7R lose 2% per decade and Z5U 5% per decade.
High K types also exhibit microphonics: they act as tiny microphones and piezo speakers!
Dielectric Absorption (sometimes called soakage) is best explained by example. charge a cap to rated voltage. Then short the leads for 1 second - then hook a voltmeter across the leads and watch as a voltage rises.
In absorption, some of the charge migrates away from the plates and slowly returns after discharge. Dielectric Absorption is not a desirable characteristic in many circuits - particularly A/D converters or sample and hold circuits. (Use polystyrene or Teflon).
There used to be some good books on passives that covered these issues - sadly they are all out of print today, but you might be able to get them at the following links.
- A Users Guide to Selecting Electronic Components by Gerald L Ginsberg
- Passive Components: a user's guide by IR Sinclair
 Imperial and metric case size codes
 By special request - milli, micro, nano, pico,
1 mili Farad (or any other unit) is 1/1,000th or .001 times the unit. (10-3)
1 micro = 1/1,000,000 or 0.000 001 times the unit (10-6 )
1 nano = 1/1,000,000,000 or 0.000 000 001 times the unit (10-9 )
1 pico = 1/1,000,000,000,000 or 0.000 000 000 001 times the unit (10-12 )
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