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Capacitor Calculator

RC timing, energy, and capacitor combinations

Time Constant (τ)

10.000 ms

Full Charge

50.000 ms

e.g. 0.000001 = 1µF

Time Constant (τ)

10.000 ms

Full Charge (5τ)

50.000 ms

Energy

12.50 µJ

Charge (Q)

5.00 µC

63% Charge

10.000 ms

Example Calculations

1RC Timing: 10kΩ + 1µF at 5V

Inputs

R10,000 Ω
C1 µF (0.000001 F)
V5 V

Result

Time Constant (τ)10.000 ms
Full Charge (5τ)50.000 ms
Energy12.50 µJ

τ = 10000 × 0.000001 = 0.01s = 10ms. 5τ = 50ms. E = 0.5 × 0.000001 × 25 = 12.5µJ.

2Parallel: 10µF + 22µF + 47µF

Inputs

Values10, 22, 47 µF
TypeParallel

Result

Total79.00 µF

Parallel: 10 + 22 + 47 = 79µF.

Frequently Asked Questions

Q

What is the RC time constant?

The time constant τ = R × C. After one τ, a capacitor charges to 63.2% of supply voltage. After 5τ, it reaches 99.3% (considered fully charged). For 10kΩ + 1µF: τ = 10ms.

  • 1τ = 63.2% charged
  • 2τ = 86.5% charged
  • 3τ = 95.0% charged
  • 5τ = 99.3% (fully charged)
Time Constants% Charged% RemainingVoltage (5V supply)
1τ63.2%36.8%3.16V
2τ86.5%13.5%4.32V
3τ95.0%5.0%4.75V
5τ99.3%0.7%4.97V
Q

How do capacitors combine in series vs parallel?

Parallel: Ctotal = C1 + C2 + C3 (add up). Series: 1/Ctotal = 1/C1 + 1/C2 + 1/C3 (reciprocal sum). Parallel increases capacitance; series decreases it but increases voltage rating.

  • Parallel: Ct = C1 + C2 (capacitance adds)
  • Series: 1/Ct = 1/C1 + 1/C2 (opposite of resistors)
  • Parallel 10µF + 22µF = 32µF
  • Series 10µF + 22µF = 6.88µF
Q

How much energy does a capacitor store?

E = ½ × C × V². A 1000µF capacitor at 5V stores 12.5mJ. Energy increases with the square of voltage—doubling voltage quadruples energy.

  • E = 0.5 × C × V²
  • 1000µF at 5V = 12.5mJ
  • 1000µF at 12V = 72mJ
  • Supercap 1F at 5V = 12.5J
Q

What is the charge stored on a capacitor?

Q = C × V. Charge in coulombs equals capacitance in farads times voltage. A 100µF cap at 10V holds 1mC (1 millichoulomb).

  • Q = C × V (charge = capacitance × voltage)
  • 100µF at 10V = 1mC
  • 1F at 5V = 5 coulombs
  • Current = charge flow: I = dQ/dt

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Last Updated: Mar 20, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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