Capacitor calculator
Read a capacitor code, find the energy it stores, or size a pair of plates.
Try 104, 104K, 229, 4n7, R50 or 100nF.
Dielectric constants are from OpenStax University Physics, Table 8.1 (room temperature).
How do I read a capacitor code like 104?
The first two digits are the value and the third says how many zeros follow; the unit is picofarads. So 104 is 10 followed by four zeros, 100,000 pF = 100 nF = 0.1 µF, and 473 is 47,000 pF = 47 nF. For small values a third digit of 9 means ×0.1 and 8 means ×0.01: 229 is 2.2 pF and 508 is 0.5 pF (KEMET). An R is a decimal point in picofarads: R50 is 0.5 pF and 2R2 is 2.2 pF (Murata).
What do the letters after the number mean?
They give the tolerance: B ±0.1 pF, C ±0.25 pF, D ±0.5 pF (under 10 pF; from 10 pF it means ±0.5%), F ±1%, G ±2%, J ±5%, K ±10%, M ±20%, and Z +80%/−20%. A 104K capacitor is 100 nF ±10%, anywhere from 90 to 110 nF; a 104Z is 100 nF with a range of 80 to 180 nF. Voltage codes such as Murata's 1H or 0J are not decoded here — read the maker's datasheet.
What do 4n7, p33 or 3µ3 mean?
The unit letter takes the place of the decimal point, as IEC 60062 has it: 4n7 is 4.7 nF, p33 is 0.33 pF, 3n3 is 3.3 nF, 33n is 33 nF and 3µ3 is 3.3 µF (Vishay). A plain 100nF or 0.1uF works too; a trailing F after the unit is read as farad, not as the ±1% letter.
How much energy does a capacitor store?
E = ½ × C × V², and the charge is Q = C × V. A 470 µF capacitor charged to 25 V holds ½ × 0.00047 × 25² = 0.147 J. Going the other way, OpenStax asks what capacitance stores 400 J at 10,000 V: C = 2E ÷ V² = 2 × 400 ÷ 10,000² = 8.00 µF — the size of a heart defibrillator's capacitor in their example.
How do I find the capacitance of two parallel plates?
C = κ × ε₀ × A ÷ d, with the plate area A, the gap d, and ε₀ = 8.854 × 10⁻¹² F/m. OpenStax's example: plates of 1.00 m² that are 1.00 mm apart in vacuum make 8.85 nF; to get a full 1 F across a 1 mm gap you would need about 1.1 × 10⁸ m², plates about 10 km on a side. A dielectric multiplies the capacitance by its constant κ: Teflon 2.1, mica 6.0, water 80 (OpenStax Table 8.1).
Sources: Murata, Chip Monolithic Ceramic Capacitors (Cat. No. C02E), Part Numbering; KEMET, C1003 C0G SMD datasheet, Ordering Information; Vishay BCcomponents, General Information, document 28536 (marking per IEC 60062 — the standard itself is paywalled, so we used the manufacturers' summaries); OpenStax University Physics Volume 2, sections 8.1, 8.3, 8.4 and 8.5 (Table 8.1); CODATA 2022 value of ε₀ (NIST). Combining capacitors? Use the series and parallel calculator; for charge time through a resistor, the RC time constant calculator. How we check our calculators.