About the Capacitor Charge Calculator
What is the Capacitor Charge Calculator?
A capacitor stores charge Q = C × V and energy ½CV². Charged through a resistor, it reaches 63% of the supply voltage after one time constant (τ = RC) and is effectively full after five.
This capacitor charge calculator gives all of these values and the voltage at any moment during charging.
How to use the Capacitor Charge Calculator
- Capacitance (µF) (sample: 470)
- Voltage (V) (sample: 12)
- Series Resistance (kΩ, for charging time) (sample: 10)
- Time Since Charging Began (ms) (sample: 1,000)
- Press Calculate Capacitor Charge (results also refresh as you type). The result card shows the Stored Charge, along with Stored energy (½CV²), Time constant (τ = RC), Time to ~99% charge (5τ) and Voltage at the time entered.
Formula used
Q = C × V; E = ½ × C × V²; V(t) = V × (1 − e^(−t/RC))
- τ = R × C = time constant in seconds
Large capacitors can hold dangerous energy – discharge them safely before handling.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Capacitance (µF) | 470 |
| Voltage (V) | 12 |
| Series Resistance (kΩ, for charging time) | 10 |
| Time Since Charging Began (ms) | 1,000 |
| Result | Value |
|---|---|
| Stored Charge | 5.64 mC |
| Stored energy (½CV²) | 0.03384 J |
| Time constant (τ = RC) | 4.7 s |
| Time to ~99% charge (5τ) | 23.5 s |
| Voltage at the time entered | 2.3 V |
| Charge level at that time | 19.2% |
Tips for using the Capacitor Charge Calculator
- Use a capacitor voltage rating at least 20–50% above the circuit voltage.
- Electrolytic capacitors have tolerances of ±20%, so time constants vary.