By Isaiah David • Updated Mar 24, 2022
Surface‑mount capacitors come in a variety of shapes and markings. Understanding how to read voltage, polarity, tolerance, and capacitance is essential for accurate component selection and reliable circuit design.
Capacitance is expressed in picofarads (pF), nanofarads (nF), or microfarads (µF). Remember: 1 000 pF = 1 nF, and 1 000 nF = 1 µF.
Example: a marking of "4.7 µF 25 V" means the capacitor stores 4.7 µF and can safely handle up to 25 volts.
Many ceramic disc capacitors use only two digits. If the value is <1, it’s in µF; if >1, it’s in pF. A marking of ".01" equals 0.01 µF (10 000 pF), while "15" equals 15 pF.
Letters indicate the unit and the decimal point. "4n7" = 4.7 nF; "p1" = 0.1 pF. This notation is common on small SMD capacitors.
Most SMD capacitors use a three‑digit code followed by a letter. The first two digits represent the significant figures, and the third is a multiplier of 10ⁿ (in pF). Example: "122" = 12 × 10² pF = 1 200 pF; "475" = 4 700 000 pF = 4.7 µF.
If the third digit is 8 or 9, the multiplier is 0.01 or 0.1, respectively. Thus, "229" = 2.2 pF.
Tolerance is denoted by a single letter: "F" = ±1%, "J" = ±5%, "K" = ±10%. For a complete tolerance chart, refer to the manufacturer’s datasheet.
These steps cover the most common labeling schemes for surface‑mount capacitors.
When replacing a capacitor, ensure the new part matches the original in type, capacitance, voltage rating, and polarity. Substituting a polarized capacitor for a non‑polarized ceramic type can lead to catastrophic failure or even explosion.
