Please enter all required numeric values.
Input Parameters Specification
VINCharging voltage applied to the capacitor in volts.
CapacitanceCapacitor value with selectable µF, nF, pF, mF or F units.
Series ResistanceResistance in the charging path, selected in Ω, kΩ or MΩ.
EnergyStored capacitor energy after charging to the entered voltage.
Time ConstantRC time constant showing how quickly the capacitor charges or discharges.
Use CaseRC timing, capacitor charging, delay circuits, filters and energy storage checks.
Formulas & Mathematical Logic
Energy = 0.5 × C × V². This calculates stored energy in joules.
Time Constant = R × C. This gives the RC time constant in seconds.
At 1τ, capacitor voltage reaches about 63% of final voltage.
At 5τ, capacitor voltage reaches about 99% of final voltage.
Step-by-Step Example
Example values: VIN = 12 V, capacitance = 1000 µF, resistance = 10 kΩ.
Convert capacitance: 1000 µF = 0.001 F.
Convert resistance: 10 kΩ = 10000 Ω.
Energy = 0.5 × 0.001 × 12² = 0.072 J.
Time Constant = 10000 × 0.001 = 10 seconds.
Practical meaning: after about 50 seconds, the capacitor is nearly fully charged.
About This Calculator
Estimate how much energy a capacitor stores and how fast it charges through a resistor.
This CalcBoy calculator finds capacitor energy and RC time constant from voltage, capacitance and resistance.
The Capacitor Charge and Time Constant Calculator is useful for RC timing circuits, power supply smoothing, soft-start circuits, reset delay networks, filters and capacitor energy storage checks. A capacitor does not charge instantly through a resistor. Instead, voltage rises gradually toward the supply voltage, while charging current starts high and falls toward zero.
Best UseRC delay circuits, timing networks, filters, capacitor charging and energy storage.
Key OutputsStored energy in joules and RC time constant in seconds.
Design BenefitQuickly compare capacitor size and resistor value before building the circuit.
Practical ReminderReal capacitors have tolerance, leakage, ESR and voltage rating limits.
The time constant is the product of resistance and capacitance. One time constant means the capacitor reaches about 63% of the supply voltage. After five time constants, it is usually considered almost fully charged. Stored energy depends strongly on voltage because voltage is squared in the energy formula.
Quick tip: increasing capacitance or resistance increases charging time, but increasing voltage greatly increases stored energy.
For real designs, check capacitor voltage rating, discharge path, inrush current, resistor wattage, leakage current and polarity. Large capacitors can store enough energy to damage components or cause sparks, so always discharge them safely before handling.
Frequently Asked Questions
What is an RC time constant?
It is the product of resistance and capacitance, showing how fast a capacitor charges or discharges.
How long does a capacitor take to charge?
After one time constant it reaches about 63%, and after five time constants it reaches about 99% of the final voltage.
What is capacitor energy?
Capacitor energy is the electrical energy stored in the electric field between capacitor plates.
Why does voltage affect energy so much?
Energy uses voltage squared, so doubling voltage increases stored energy by four times.
Can I use this for discharge time?
Yes. The same RC time constant applies to capacitor discharging through a resistor.
Does this include ESR or leakage?
No. It uses ideal formulas. Real capacitors may have ESR, leakage and tolerance effects.