Electric Charge Calculator (Q = I × t)
What is an electric charge calculator?
A charge calculator helps you determine how much electric charge moves through a circuit over time. The basic relationship is simple: current multiplied by time equals charge. This is one of the most useful equations in practical electronics, battery analysis, physics homework, and lab work.
If you know how much current is flowing and for how long it flows, you can instantly estimate total charge in coulombs. From there, it is easy to convert to amp-hours, milliamp-hours, or even estimate how many electrons were transferred.
The core formula
Q = I × t
- Q = charge (coulombs, C)
- I = current (amperes, A)
- t = time (seconds, s)
For example, if a circuit draws 2 A for 10 s, then: Q = 2 × 10 = 20 C.
How to use this charge calculator
- Enter a current value.
- Select the current unit (A, mA, µA, or kA).
- Enter a time value.
- Select the time unit (seconds, milliseconds, minutes, hours, or days).
- Click Calculate Charge to see results and conversions.
The tool converts your inputs into SI units behind the scenes, then computes charge in coulombs. It also shows: amp-hours, milliamp-hours, and an estimate of transferred electrons.
Why unit conversion matters
Many mistakes come from mixing units. A few examples:
- 500 mA is 0.5 A, not 500 A.
- 2 minutes is 120 seconds.
- 1 mAh corresponds to 3.6 C.
Good calculators handle conversion automatically so you can focus on understanding the system, not manual arithmetic.
Practical examples
1) Battery-powered sensor
A sensor draws 120 mA for 45 minutes. Convert: 120 mA = 0.12 A, 45 min = 2700 s. Charge is 0.12 × 2700 = 324 C.
2) Fast charging estimate
A charger supplies 3 A for 20 minutes. Convert 20 min = 1200 s. Charge is 3 × 1200 = 3600 C, which equals 1 Ah.
3) Tiny current over long duration
A low-power device consumes 250 µA for 7 days. This seems tiny, but over long periods the total charge can become significant.
Common pitfalls to avoid
- Entering negative time (time should be positive).
- Forgetting to convert minutes or hours to seconds in manual calculations.
- Confusing power (watts) with charge (coulombs).
- Assuming current remains constant when it may vary in real circuits.
Final note
A charge calculator is a quick, practical way to connect theory with real-world electrical behavior. Whether you are studying physics, designing embedded systems, or working with battery runtime estimates, the equation Q = I × t is a dependable first step.