Capacitor calculator
Pick a mode: combine capacitors, find energy and charge, work out an RC time constant and reactance, or decode a printed code like 104.
VC-20 capacitorC · E · τ · CODE
Mode
Connection
F
e.g. 10u, 100n, 4.7pF
e.g. 10u, 100n, 4.7pF
e.g. 10u, 100n, 4.7pTotal capacitance32 µF
Capacitor formulas
- Parallel: C = C1 + C2 + … (voltage rating = lowest of the parts)
- Series: 1/C = 1/C1 + 1/C2 + … (voltage divides; add balancing resistors for electrolytics)
- Energy: E = ½ C V². Charge: Q = C V
- Time constant: τ = R C; the capacitor reaches 63.2% in one τ and about 99.3% in 5τ
- Reactance: Xc = 1 ÷ (2π f C). RC cutoff: fc = 1 ÷ (2π R C)
Reading capacitor codes
Small ceramic and film capacitors use three digits: two significant figures and a multiplier, in picofarads. 104 = 10 × 10⁴ pF = 100 nF. 472 = 4.7 nF. A letter after the code is often tolerance: J = ±5%, K = ±10%, M = ±20%.
Questions people ask
How do capacitors add in series and parallel?
Opposite to resistors: in parallel they add (C = C1 + C2); in series 1/C = 1/C1 + 1/C2.
What does 104 mean on a capacitor?
The first two digits are the value and the third is the number of zeros, in picofarads: 10 × 10⁴ pF = 100,000 pF = 100 nF = 0.1 µF.
How much energy does a capacitor store?
E = ½ × C × V². A 1,000 µF capacitor at 50 V stores 1.25 J. Large capacitors can hold a dangerous charge after power is removed; discharge them safely before handling.