Calculator
Example data
These examples help you verify expected outputs.
| Voltage (V) | Current (A) | Resistance (Ω) | Power (W) |
|---|---|---|---|
| 12 | 1.5 | 8 | 18 |
| 5 | 0.25 | 20 | 1.25 |
| 230 | 2 | 115 | 460 |
Formula used
- Ohm’s Law: V = I × R
- Current: I = V ÷ R
- Resistance: R = V ÷ I
- Power: P = V × I = I² × R = V² ÷ R
- Energy (optional): E = P × t
For AC calculations, use RMS voltage and RMS current.
How to use this calculator
- Select a mode. Auto mode solves any missing V, I, or R.
- Enter any two of Voltage, Current, and Resistance.
- Pick units that match your measurements.
- Optionally add time to compute energy usage.
- Press Calculate to see results above the form.
- Use CSV or PDF buttons to export the latest result.
FAQs
1) What values do I need to calculate the third one?
Provide any two of voltage, current, and resistance. The calculator uses Ohm’s law to solve the missing value and then computes power automatically.
2) Can I calculate power without entering all three values?
Yes. Power is calculated from whichever valid pair you provide: V and I, I and R, or V and R. If no valid pair is available, power is not shown.
3) What does the AC (RMS) option change?
It changes labeling only. Use RMS voltage and RMS current for AC circuits. The same equations apply when values represent RMS measurements.
4) Why do I see an inconsistency warning?
If you enter V, I, and R together, the calculator checks whether V ≈ I×R. A mismatch suggests measurement error, rounding, or a non-ohmic load.
5) How is energy computed?
If you enter time, energy is computed using E = P × t. You can display energy in joules, kilojoules, or watt-hours for convenience.
6) What units are supported?
Voltage supports mV, V, and kV. Current supports µA, mA, and A. Resistance supports mΩ, Ω, kΩ, and MΩ. Time supports seconds, minutes, and hours.
7) What should I do if resistance is zero?
A zero resistance value can cause division-by-zero when solving for current or power with V²/R. Use a realistic resistance, or switch modes and enter different known values.
8) Are the results suitable for safety-critical design?
Use results as a quick engineering check. For real designs, verify component ratings, temperature rise, tolerances, and protective devices before building or testing hardware.