Unlike resistors, capacitors use a variety of codes to describe their characteristics. Small physical capacitors are very difficult to read because of limited space for printing text. The information in this article will help you read almost all modern consumer capacitors. Don't be surprised if the information listed on the capacitor is different from what is described in this article, or if the voltage and tolerance information isn't written on the capacitor. For many low-voltage homemade electrical circuits, you only need the capacitance information.
Method 1 of 2: Reading Large Capacitors
Step 1. Know the units of measurement for capacitors
The unit of measure for capacitance is the farad (F). This value is too large for large electrical circuits, so household capacitors are labeled with one of the following units:
- 1 F, uF, or mF = 1 microfarad = 10-6 farads. (Careful, in other contexts mF is the official abbreviation for millifarad, or 10-3 farads.)
- 1 nF = 1 nanofarad = 10-9 farads.
- 1 pF, mmF, or uuF = 1 picofarad = 1 micromicrofarad = 10-12 farads.
Step 2. Read the capacitance value
Most capacitors have a capacitance value listed on their side. Usually there is a slight variation in the text so look for the value closest to the unit above. You may need to make some of the following adjustments:
- Ignore capital letters in units. For example, "MF" is simply a variation of "mf" (and no the same as megafarad, although MF is the official abbreviation).
- Don't be confused by "fd." This is just another abbreviation of farad. For example, "mmfd" is the same as "mmf."
- Watch out for single-letter markings, such as "475m," which are commonly found on small capacitors. See below for further instructions.
Step 3. Find the tolerance value
Some capacitors list tolerances, or the approximate range of maximum capacitance compared to the listed values. Not all electrical circuits require tolerances. For example, a capacitor labeled "6000uF +50%/-70%" could actually have a capacitance of 6000uF + (6000 * 0.5) = 9000uF, or as small as 6000 uF - (6000uF * 0.7) = 1800uF.
If no percentage is listed, look for one letter after the capacitance value or in its own line. This can be a tolerance value code, which will be explained below
Step 4. Check the voltage rating
Where possible, the manufacturer will list a number on the capacitor followed by the letters V, VDC, VDCW, or WV (for "Working Voltage"). This is the maximum voltage the capacitor can handle.
- 1 kV = 1000 volts.
- Look below if you think the capacitor uses a code for voltage (one letter, or one digit number and one letter). If there is absolutely no symbol, it is better if the capacitor is only used in low-voltage electrical circuits.
- If you're building an AC circuit, look for capacitors specifically designed for VAC. Do not use DC capacitors unless you have knowledge and experience with changing voltage ratings, and how to use them safely in AC devices.
Step 5. Look for the + or - symbol
If you see one of these next to the terminals, it means the capacitor is polarized. Make sure you connect the + pole of the capacitor with the positive side of the electrical circuit. Otherwise, the capacitor may short circuit or even explode. If you don't see a + or - sign, it means the capacitor is bidirectional.
Some capacitors use colored stripes or ring-shaped depressions to indicate polarity. In the past, this mark marked the – end of the aluminum electrolytic capacitor (usually shaped like a can). On tantalum electrolytic capacitors (which are very small, this mark indicates the + end. (Ignore the line if the + and – signs do not match, or the capacitor is a nonelectrolyte type)
Method 2 of 2: Reading Compact Capacitor Codes
Step 1. Write down the first two digits of the capacitance
Old capacitors are more difficult to predict, but almost all modern examples use standard EIA codes when the capacitor is too small to list the entire capacitance. To get started, write down the first two digits, then specify the next step according to the following code:
- If the exact code starts with two digits, followed by a letter (for example, 44M), the first two digits are the full capacitance code. Go directly to the "find units" section.
- If one of the first two characters is a letter, go directly to the "letter system".
- If all the first three characters are numbers, continue to the next step.
Step 2. Use the first three digits as a zero multiplier
The three-digit capacitance code works as follows:
- If the third digit number is between 0-6, add as many zeros as the number to the end of the first two digits (for example, the code is 453 → 45 x 103 → 45.000.)
- If the third digit is 8, multiply by 0.01. (for example, 278 → 27 x 0.01 → 0.27)
- If the third digit is 9, multiply by 0, 1. (eg 309 → 30 x 0, 1 → 3, 0)
Step 3. Work out the capacitance units from the context. The smallest capacitors (made of ceramic, film, or tantalum) use picofarad units (pF) which are equal to 10-12 farads. Large capacitors (with a cylindrical or double-coated aluminum electrolyte type) use units of microfarads (uF or F), the value of which is equal to 10-6 farads.
A capacitor can override this by adding a unit behind it (p for picofarad, n for nanofarad, or u for microfarad). However, if after the code there is only one letter, this is usually the tolerance code for the capacitor, and not representing the unit. (P and N are rarely encountered tolerance codes, but there are capacitors that list them)
Step 4. Read the code containing the letters
. If your code lists a letter as one of the first two characters, there are three possibilities:
- If the letter is R, replace it with a decimal point to get the capacitance in pF units. For example, 4R1 means the capacitance is 4.1pF.
- If the letters are p, n, or u, they all represent units (pico-, nano-, or microfarads). Replace this letter with a decimal point. For example, n61 means 0.61 nF, and 5u2 means 5.2 uF.
- A code like "1A253" is actually two codes. 1A represents voltage, and 253 represents capacitance as described above.
Step 5. Read the tolerance code on the ceramic capacitor
Ceramic capacitors, which are usually two "pan cakes" with two pins, often include a tolerance value of one letter after the three-digit capacitance value. This letter reflects the tolerance of the capacitor, which means the approximate closeness of the actual value of the capacitor to the value listed on the capacitor. If your electrical circuit requires precision, translate this code in the following way:
- B = ± 0.1 pF.
- C = ± 0.25 pF.
- D = ±0.5 pF for capacitors rated below 10 pF, or ±0.5% for capacitors above 10pF.
- F = ±1 pF or ±1% (use the same reading system as D above).
- G = ±2 pF or ±2% (see above).
- J = ± 5%.
- K = ± 10%.
- M = ± 20%.
- Z = +80% / -20% (If you see no tolerance code, assume this value is the worst case scenario.)
Step 6. Read the letter-number-letter tolerance value
Many capacitor types include a tolerance code with a more detailed three-symbol system. Interpret this code as follows:
- The first symbol indicates the minimum temperature. Z = 10ºC, Y = -30ºC, X = -55ºC.
- The second symbol indicates the maximum temperature.
Step 2. = 45ºC
Step 4. = 65ºC
Step 5. = 85ºC
Step 6. = 105ºC
Step 7. = 125ºC.
- The third symbol shows the variation in capacitance throughout this temperature range. This range starts with the most accurate, A = ±1.0%, down to least accurate, V = +22, 0%/-82%. R, one of the most frequently occurring symbols, shows a variation of ±15%.
Step 7. Translate the voltage code. You can look it up on the EIA voltage chart, but most capacitors use one of the following codes to indicate the maximum voltage (the following values are for DC capacitors only):
- 0J = 6, 3V
- 1A = 10V
- 1C = 16V
- 1E = 25V
- 1H = 50V
- 2A = 100V
- 2D = 200V
- 2E = 250V
- The one-letter code stands for one of the common values above. If multiple capacitor values are applicable (eg 1A or 2A), you need to work from context.
- For other, less frequently encountered code estimates, see the first digit. The number 0 includes values less than 10, 1 covers 10-99, 2 covers 100 to 999, and so on.
Step 8. Look for another system
old capacitors or those specially made for specialists can use a different system. This system is not discussed in this article, but you can use the following instructions for further research:
- If the capacitor has a long code starting with "CM" or "DM," look it up on the US military capacitor chart.
- If the capacitor is not coded, but rather a series of colored bands or dots, look up the color code of the capacitor.
- Capacitors can also include operating voltage information. Capacitors must support a higher voltage than the electrical circuit used. Otherwise, the capacitor may be damaged (or even exploded) during operation.
- 1,000,000 picoFarad (pF) is equal to 1 microFarad (µF). Many capacitor values are close to these two units so their use is often interchangeable. For example, 10,000 pF is more often written as 0.01 uF.
- While you can't determine capacitance by the shape and size of the capacitor, you can guess roughly by how the capacitor is used:
- The largest capacitor in the television monitor is in the power supply. Each capacitor has a capacitance as high as 400 to 1,000 F, which can be dangerous if handled carelessly.
- The large capacitors in vintage radios typically have a range of 1-200 F.
- Ceramic capacitors are usually smaller than a thumb and are attached to an electrical circuit with two pins. These capacitors are used in many devices and usually have a range of 1 nF to 1 F, although some go as high as 100 F.