Small ceramic chip capacitors on laptop boards carry no marking at all, so their value comes from the schematic. But film, tantalum, polymer, through-hole ceramic and some larger SMD capacitors do carry a code. This decoder reads the common formats and converts the result into picofarads, nanofarads and microfarads, because different parts lists use different units for the same value.
How to use it
Type the code as printed: 104, 225K, 4n7, 47p, 0.1 or a full film-capacitor marking such as 2A104J. Read the capacitance, the same value in other units, the tolerance and, if present, the voltage rating.
The marking formats
| Format | Example | Meaning |
|---|---|---|
| 3-digit code (pF) | 104 | 10 × 10⁴ pF = 100 nF = 0.1 µF |
| Letter as decimal point | 4n7, 2u2, 47p | 4.7 nF, 2.2 µF, 47 pF |
| Plain decimal | 0.1 | Usually µF |
| Small number | 47 | pF |
| Tolerance letter after the value | 104K | K = ±10 % |
| EIA voltage code before the value | 2A104J | 2A = 100 V, 100 nF, J = ±5 % |
The third digit of a 3-digit code is the number of zeros after the first two digits, in picofarads. Two special cases: 8 means ×0.01 and 9 means ×0.1, for values below 10 pF.
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 %.
Worked example
A yellow film capacitor in a desktop power supply is marked 2A473J. 2A is the EIA code for 100 V; 473 is 47 × 10³ pF = 47 nF; J is ±5 %. A replacement must be at least 47 nF, ±5 %, rated 100 V or more, of the same type.
Tantalum and polymer codes
Tantalum and polymer chips often print the value and voltage more directly, for example 107 with a voltage letter, or 220 6.3. The value part decodes the same way: 107 is 10 × 10⁷ pF = 100 µF. Manufacturer-specific voltage letters vary, so check the datasheet when in doubt. Testing these parts is covered in How to Test a Capacitor with a Multimeter, and the component under polymer capacitor.
FAQ
Why are most laptop capacitors unmarked?
Ceramic chips in 0402 and smaller sizes are too small to print on. The schematic and boardview identify them.
Is 104 the same as 0.1 µF?
Yes: 100,000 pF = 100 nF = 0.1 µF.
What does the letter after the number mean?
Usually tolerance (K, J, M). A letter-digit pair before the number, like 2A, is usually the voltage code.