Capacitance Calculator
The charge tank: C = Q/V from a measured charge and voltage, the stored energy at half C-V-squared, and the combining rules that invert the resistor book.
Capacitance Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Linear, temperature-stable dielectric assumed
- No ESR, leakage or dielectric breakdown
In short: Park 0.01 C of charge on a capacitor at 100 V and you have measured C = Q/V = 0.000100 F = 100.000000 µF. The bank card prices the storm it holds: E = ½CV² = 0.500000 J — camera-flash scale, released in a blink. The combining card is the one that bites: two of these in PARALLEL hold 2C = 200.000000 µF, in SERIES only 50.000000 µF — the exact inverse of the resistor book, because plates side by side pool their area while end-to-end share the same charge.
Formula
C = Q / V · E = ½CV² · parallel: C₁+C₂ · series: reciprocal of the reciprocals
Capacitance is a tank rating: coulombs stored per volt of push. The energy is half the product C-V-squared — the half is the signature of charging against a rising push, the same area-under-the-curve half as the spring page's ½kx². Combining goes opposite to resistors because the geometry decides: parallel plates pool area, series plates pass the same charge along.
Worked Example
- Enter the charge you parked and the voltage it sits at.
- Read C in farads and microfarads.
- Read the energy bank — what the discharge can pay out.
- Combine capacitors with the INVERTED rules; check the card before wiring packs.
Defaults: 100.000000 µF; bank 0.500000 J; parallel 2C = 200.000000 µF, series 50.000000 µF.
Strengths & Limits Of This Model
Where this engine is strong
- Combining rules computed with the inversion named
- Energy bank priced from your own measurement
Where it stops
- No ripple or AC reactance
- No voltage-rating safety check
Practical Use Cases
Electronics
reading and sizing caps from measurements
Flash and pulse
energy banked per shot
Teaching
why cap rules invert resistor rules
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Capacitance Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why do capacitors combine opposite to resistors?
Geometry. Parallel plates add AREA side by side, and capacitance grows with area — so parallel caps add. Series caps pass the same charge along through thinner effective gaps, and thinner gaps mean MORE capacitance per stage... divided across the stack, the stack holds less than the smallest piece. The card computes both from your own C.
Where does the half in ½CV² come from?
From charging: each coulomb lands at a slightly higher push than the last, so the total work is the area under a rising line — a triangle, half the rectangle. The same half appears in the spring page's ½kx²: both store energy against a restoring push that grows as it fills.
Why must the charge be positive to measure?
Because C = Q/V is a MEASUREMENT: a capacitor with no charge on it tells you nothing about its tank, the way an empty bucket cannot report its capacity. Park a measured charge, read the push, divide — the page refuses the zero-charge version rather than grade a non-measurement.
What does the voltage rating mean, physically?
The dielectric's breaking point — exceed it and the insulator between the plates conducts, sometimes violently. The rating lives outside C = Q/V (which is the tank's size, not its strength), but the energy card shows why overstressed caps fail loud: banked energy goes somewhere.
Is a farad big or small?
Huge. Everyday caps are microfarads (millionths) and picofarads (trillionths); a full farad is a supercapacitor. The default here — 100 µF — is already a substantial electrolytic, and it banks half a joule: enough to fire a flash, not enough to turn an engine.
Where does the charge go when the cap discharges?
Through whatever path you give it, at a rate set by resistance times capacitance — the RC time constant. Fast into a flash tube, slow into a filter, and never instantly: even a shorted cap spends its bank through the wires' own resistance.
Does temperature change capacitance?
Slightly — dielectric constants drift with temperature, some ceramic formulations notoriously so. The page prices the nominal tank; precision timing circuits pick dielectrics precisely because this drift is real.
How does this pair with the voltage page?
Through the promise: voltage is energy per charge, and the bank card is exactly that promise multiplied out — ½CV² is the energy each coulomb collects on average while the tank fills. Two pages, one bookkeeping.