Capacitor CalculatorSeries · parallel · Q = CV · RC
Capacitors in parallel add (C = C₁ + C₂ + …), while in series their reciprocals add (1/C = 1/C₁ + 1/C₂ + …), the opposite of resistors. A capacitor stores charge Q = CV and energy E = ½CV². Combine up to four capacitors, find the charge and energy at a voltage, or get an RC circuit’s time constant (τ = RC) and cutoff frequency, with a live charging curve.
Formula verified against OpenStax — University Physics, Volume 2 · OpenStax — University Physics, Volume 2
By Manzoor Ahmad · Pharmacist & calculator developerReviewed & updated
Capacitor values
Enter capacitance in pF, nF, µF or F. Leave unused capacitors at 0.
Step-by-step working
What is capacitor?
A capacitor is a component that stores electrical energy in an electric field between two conductive plates separated by an insulator. Its capacitance, measured in farads, is the charge it stores per volt.
Capacitors smooth power supplies, block DC while passing AC signals, set timing in RC circuits, tune radios, and deliver the bursts of energy behind camera flashes and defibrillators.
Quick answers
How do you calculate capacitors in series?
Add the reciprocals and invert: 1/C = 1/C₁ + 1/C₂. Two 100 µF capacitors in series give 50 µF, with double the voltage rating.
How do you calculate capacitors in parallel?
Simply add them: 22 µF + 47 µF = 69 µF. Each capacitor sees the full voltage.
How much energy does a capacitor store?
E = ½CV². A 330 µF camera-flash capacitor at 300 V stores 14.85 J, released in about a millisecond.
What is the RC time constant?
τ = R × C, the time to charge to 63.2% (or discharge to 36.8%). 10 kΩ with 100 nF gives 1 ms, typical for switch debouncing. Convert the cutoff to a period with the frequency calculator.
Capacitor formulas
Charging: V(t) = V₀(1 − e−t/τ). Discharging: V(t) = V₀e−t/τ.
| Symbol | Meaning | SI unit |
|---|---|---|
| C | Capacitance | F |
| Q | Charge | C (coulombs) |
| V | Voltage | V |
| E | Stored energy | J |
| R | Resistance | Ω |
| τ | Time constant | s |
How to calculate capacitors in series and parallel
- Convert every value to the same unit (µF, say).
- Parallel: add them up.
- Series: add the reciprocals, then take the reciprocal of the sum.
- Check voltage ratings: parallel is limited by the lowest rating; in series the ratings add, if the capacitors are balanced.
Worked example: 10, 22 and 47 µF
Three capacitors of 10 µF, 22 µF and 47 µF are combined.
Series: 1/C = 1/10 + 1/22 + 1/47 → C = 5.998 µF
A 1,000 µF capacitor charged to 25 V holds Q = 25 mC and E = ½ × 0.001 × 25² = 0.3125 J. A 10 kΩ resistor with 100 µF gives τ = 1.0 s and a cutoff frequency of 0.159 Hz.
Capacitor unit prefixes
Common markings and what they mean.
| Marking | Value | Typical use |
|---|---|---|
| pF (picofarad) | 10⁻¹² F | RF tuning, oscillators |
| nF (nanofarad) | 10⁻⁹ F | Decoupling, filters |
| µF (microfarad) | 10⁻⁶ F | Power supply smoothing |
| mF (millifarad) | 10⁻³ F | Large electrolytics |
| F (farad) | 1 F | Supercapacitors |
| Code “104” | 10 × 10⁴ pF = 100 nF | Ceramic capacitor label |
Common mistakes to avoid
- Combining capacitors like resistors. The rules are swapped: parallel adds, series uses reciprocals.
- Exceeding the voltage rating. Electrolytic capacitors can vent or explode when over-voltaged or reversed.
- Assuming a capacitor is safe once unplugged. Discharge large capacitors through a resistor before touching them.
Manzoor Ahmad
Pharmacist turned Web Developer & Calculator Engineer · 13+ years in web developmentI’m a pharmacist by training who turned into a full-time tech geek, and for 13+ years I’ve designed and coded web tools. My pharmacy degree included physical pharmacy and pharmaceutics — states of matter, heat, flow and reaction kinetics — so the physics behind these tools is familiar ground, not a new hobby.
I’m not a physicist, so I don’t ask you to take my word for it: every formula on this page is traced to an open university textbook or NIST reference data, and the calculator is tested against published worked examples before it goes live. Spot an error? Tell me and it will be fixed and dated on the next update.
Capacitor Calculator: frequently asked questions
1/Ctotal = 1/C₁ + 1/C₂ + … For two capacitors, C = C₁C₂ ÷ (C₁ + C₂).
Ctotal = C₁ + C₂ + C₃ + …
Q = CV. A 100 µF capacitor at 12 V holds 1.2 mC.
τ = RC in seconds (with ohms and farads). It is the time to reach 63.2% of the final voltage while charging.
Putting capacitors in series is like increasing the gap between the plates, which reduces capacitance.
References & sources
- OpenStax — University Physics, Volume 2 — Ch. 8, Capacitance (8.2 Capacitors in Series and Parallel, 8.3 Energy Stored)
- OpenStax — University Physics, Volume 2 — Ch. 10.5, RC Circuits
- HyperPhysics, Georgia State University — capacitors
Disclaimer: This calculator is an educational tool built on idealised textbook models. It is not a substitute for professional engineering or safety calculations.