Capacitance Calculator
Compute C from charge and voltage (optional: R, f)
Tip: C = Q / V. Add R for τ, add f for Xc.
Capacitance (F)
0
Capacitance (friendly)
0
Voltage (V)
0
Stored Energy E (J) = ½·C·V²
0
Time Constant τ (s) = R·C
—
Reactance Xc (Ω) = 1/(2πfC)
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Calculate

Capacitance Calculator pages are most useful when they do two things well: explain the idea clearly and walk you through clean inputs and outputs. This guide does both, so you can calculate capacitor values confidently and avoid common mistakes.

What is a Capacitance Calculator?

A Capacitance Calculator estimates the capacity of a component to store electric charge. In simple terms, capacitance is the ratio of stored charge to voltage :

C=QVC = \frac{Q}{V}

The SI unit is the farad (F). In practice you’ll often see microfarads (µF), nanofarads (nF), or picofarads (pF). A calculator can also convert between these units and apply series/parallel rules.

How to Use the Capacitance Calculator — Step by Step

  1. Choose what you’re solving for. Most tools let you pick , , or . If you have any two, the calculator finds the third.

  2. Enter known values with units. For example, Q=240 μCQ = 240\ \mu\text{C} and V=12 VV = 12\ \text{V}. The Capacitance Calculator should handle prefixes like µ, n, and p automatically.

  3. Calculate. Using C=Q/VC = Q/V, the result here is 20 μF20\ \mu\text{F}.

  4. Refine with geometry (optional). If you’re designing a capacitor, some calculators estimate CC from plate area AA, separation dd, and material permittivity ε\varepsilon:

    C=εAdC = \varepsilon \frac{A}{d}

    With a dielectric, ε=ε0εr\varepsilon = \varepsilon_0 \varepsilon_r.

  5. Convert units. Keep results consistent—e.g., 0.02 mF=20 μF0.02\ \text{mF} = 20\ \mu\text{F}. A unit switcher inside the Capacitance Calculator saves time.

Series and Parallel Combinations (Calculator Shortcuts)

  • Series:

    1Ceq=∑1Ci\frac{1}{C_\text{eq}} = \sum \frac{1}{C_i}

    Series lowers the total capacitance—useful for higher voltage ratings.

  • Parallel:

    Ceq=∑CiC_\text{eq} = \sum C_i

    Parallel increases the total—great when you need more smoothing in power supplies.

Good Capacitance Calculator tools let you enter a list like “10 µF, 10 µF, 4.7 µF” and instantly see CeqC_\text{eq} for either arrangement.

Practical Tips for Accurate Results

  • Mind tolerances. Common electrolytics can be ±20%. If your design is tight, select better-tolerance film or C0G/NP0 ceramics.

  • Watch voltage rating. Pick a capacitor with a rating well above operating voltage (often 2× as a rule of thumb).

  • Account for temperature and bias. Some ceramic dielectrics lose capacitance under DC bias; your Capacitance Calculator result is the ideal value, so check real-world derating curves.

  • ESR and ripple matter. In power circuits, equivalent series resistance affects heat and ripple; calculator outputs are the starting point, not the whole story.

Worked Example (Parallel + Unit Conversion)

You need about 22 μF22\ \mu\text{F} for a microcontroller power rail but only have 10 μF10\ \mu\text{F} and 4.7 μF4.7\ \mu\text{F} parts. Using the Capacitance Calculator, enter a parallel set: 10 μF+10 μF+4.7 μF10\ \mu\text{F} + 10\ \mu\text{F} + 4.7\ \mu\text{F} → 24.7 μF24.7\ \mu\text{F}. If your tool reports 0.0247 mF0.0247\ \text{mF}, convert inside the calculator to μF\mu\text{F} so the result matches your BOM.

Geometry-Based Estimation (For Learning and Prototyping)

For two plates in air: C=ε0A/dC = \varepsilon_0 A/d. Suppose A=0.01 m2A = 0.01\ \text{m}^2 and d=1 mm=0.001 md = 1\ \text{mm} = 0.001\ \text{m}. With ε0≈8.85×10−12 F/m\varepsilon_0 \approx 8.85\times10^{-12}\ \text{F/m}, the Capacitance Calculator gives C≈88.5 pFC \approx 88.5\ \text{pF}. Add a dielectric with εr=4\varepsilon_r = 4 and you’re near 354 pF354\ \text{pF}.

Common Questions About the Capacitance Calculator

Is the Capacitance Calculator accurate?
It’s exact for the underlying formulas. Real parts vary with tolerance, temperature, and frequency. Cross-check with a meter when precision matters.

Can I mix types?
Yes, but mixing electrolytic and ceramic in parallel can shift behavior across frequencies. Use the Capacitance Calculator for totals, then verify stability on the bench.

What about frequency?
Ideal formulas are frequency-independent, but real capacitors change impedance with frequency. Your calculator’s capacitance is the DC/small-signal value.

Helpful Resources and Related Tools

Capacitance Calculator for series and parallel combinations
Enter charge and voltage to find C, or combine capacitors in series or parallel.

Internal tools to speed up your workflow:

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