Calculate capacitance from stored charge and voltage, or combine multiple capacitors in series or parallel.
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Capacitance measures a capacitor's ability to store electrical charge at a given voltage difference, and it's calculated from the basic relationship C = Q ÷ V, where Q is the amount of stored charge and V is the voltage difference across the capacitor's terminals. When more than one capacitor is connected together, calculating the total capacitance differs depending on the connection method: in parallel, capacitances are added directly (C_total = C1 + C2 + ...), because each capacitor stores additional charge at the same voltage; while in series, the reciprocals of the capacitances are added (1/C_total = 1/C1 + 1/C2 + ...), with the resulting total capacitance always being smaller than the smallest individual capacitance in the group — the same principle used in calculating parallel resistors, but in reverse order, since capacitors in series behave like resistors in parallel, mathematically. This inverse relationship between capacitor and resistor combination rules is one of the more elegant symmetries in basic circuit theory, and understanding it helps avoid a common source of error when analyzing mixed component networks.
Anyone learning basic circuit theory eventually notices a pattern that seems backwards at first: resistors in series simply add together, while resistors in parallel combine through reciprocals — but capacitors do exactly the opposite, adding directly in parallel and combining through reciprocals in series. This isn't an arbitrary rule to memorize; it follows directly from what each component actually does physically.
A resistor in series with another resistor forces current through both, one after another, and each adds its own opposition to that current — so total resistance is simply the sum. A capacitor works differently: it's fundamentally a charge-storage device, and when two capacitors are connected in parallel, both are exposed to the identical voltage and each stores its own charge independently, so the total charge storage capacity (and therefore total capacitance) is simply the sum of both.
In series, capacitors behave less intuitively: the same charge has to flow through both capacitors sequentially, and the voltage divides between them rather than being identical across each — the capacitor with smaller capacitance ends up holding proportionally more voltage for the same charge, which is exactly the physical relationship the reciprocal formula captures. The result is always a smaller combined capacitance than the smallest individual capacitor in the series chain, mirroring how parallel resistors always produce a resistance smaller than the smallest individual resistor.
This symmetry — series capacitors mathematically mirroring parallel resistors, and parallel capacitors mirroring series resistors — isn't a coincidence; it emerges from the underlying physics, where capacitance is inversely related to the 'stiffness' a component presents to charge storage in a way that's mathematically dual to how resistance relates to current flow. Recognizing this duality helps when quickly sanity-checking a calculation: if a series capacitor combination gives an answer larger than the smallest individual value, something in the calculation has gone wrong.
Practically, this matters for circuit designers combining standard-value capacitors to reach a non-standard target capacitance, or for anyone analyzing existing multi-capacitor circuits like power supply filter banks, where capacitors are frequently combined in both series and parallel configurations to balance the total capacitance against voltage rating requirements, since capacitors in series also share the total applied voltage across them, which allows using standard-voltage-rated capacitors in circuits that would otherwise require a higher voltage rating than any single component provides.
Because capacitance measures stored charge per volt rather than resistance to current flow — adding parallel capacitor plates increases total charge storage area, while series connections effectively increase plate separation, reducing total capacitance.
Charge is entered in microcoulombs (μC) and capacitance in microfarads (μF), the most common practical units for everyday electronics; for very large or small values, convert to/from farads by multiplying or dividing by 1,000,000.
This tool supports up to three capacitors per calculation for clarity; for larger banks, combine them in pairs step by step using the result of one calculation as an input to the next.