Ohm's Law Calculator
Enter any 2 values — the third will be calculated
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = IR. It is the foundation of electrical circuit analysis. Power (P = VI = I²R = V²/R) describes the energy converted per second.
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Tip: Most household circuits are 15A (US) or 20A. A 15A/120V circuit can handle up to 1,800W. Running appliances above this trips the circuit breaker.
- 1Identify any two known values: voltage (V), current (A), or resistance (Ω)
- 2Rearrange: V = IR, I = V/R, R = V/I
- 3Calculate power: P = V × I = I²R = V²/R
- 4Apply units: Volts (V), Amperes (A), Ohms (Ω), Watts (W)
12V battery, 4Ω resistance=I = 3A, P = 36WI = 12/4 = 3A, P = 12×3 = 36W
120V outlet, 10A circuit=R = 12Ω, P = 1,200WA typical 1,200W microwave
| Find | Formula 1 | Formula 2 |
|---|---|---|
| Voltage (V) | V = I × R | V = P / I |
| Current (I) | I = V / R | I = P / V |
| Resistance (R) | R = V / I | R = V² / P |
| Power (P) | P = V × I | P = I² × R |
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Fun Fact
Georg Ohm published his law in 1827. It was initially rejected by scientists — the Royal Society awarded him the Copley Medal 14 years later once it was proven experimentally valid.
References
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