Solve any electrical unknown. This free Ohm’s law calculator takes any two of voltage, current, resistance or power and computes the other two using V = I x R and P = V x I.
Fill in any two values and the calculator works out the rest using Ohm’s law (V = I x R) and the power law (P = V x I). Enter exactly two to solve.
Ohm’s law: V = I x R. Power: P = V x I (also P = I²R = V²/R). Voltage in volts, current in amps, resistance in ohms (Ω), power in watts.
How the Ohm’s Law Calculator Works
Ohm’s law links voltage, current and resistance in any electrical circuit, and the power law adds how much energy that circuit uses per second. Enter any two known values and the calculator solves for the rest.
Formula: Voltage = Current × Resistance (V = I × R). Power = Voltage × Current (P = V × I), which can also be written as P = I² × R or P = V² ÷ R. Voltage is in volts, current in amps, resistance in ohms (Ω), and power in watts.
- V (Voltage) — the value entered in the Voltage field, in volts
- I (Current) — the value entered in the Current field, in amps
- R (Resistance) — the value entered in the Resistance field, in ohms
- P (Power) — the value entered in the optional Power field, in watts, or the value the calculator computes from V and I
Example Scenarios
| Voltage (V) | Resistance (Ω) | Current (A) |
|---|---|---|
| 10 | 2 | 5 |
| 12 | 4 | 3 |
| 20 | 5 | 4 |
| 9 | 9 | 1 |
| 48 | 6 | 8 |
Ohm’s Law Calculator FAQ
Which two values do I need to enter?
Any two of Voltage, Current, or Resistance are enough — the calculator solves for whichever one you leave blank using V = I × R. You can also enter Power alongside one other value if you don’t have two of V, I, and R.What happens if I fill in all four fields?
The hint on the calculator asks for exactly two values so the math has a single, unambiguous solution. Filling in more can conflict with what the other two imply, so it’s best to clear a field before recalculating.How is power related to voltage and current?
Power equals voltage multiplied by current (P = V × I). Substituting Ohm’s law for I or V also gives the equivalent forms P = I² × R and P = V² ÷ R, which the calculator can use to fill in Power alongside Voltage, Current, and Resistance.Does this calculator work for AC circuits?
The V = I × R relationship shown here applies directly to DC circuits and to AC circuits with purely resistive loads. AC circuits with inductors or capacitors involve impedance and phase angles, which this simple calculator doesn’t account for.What’s a typical resistance value for a household device?
It varies enormously by device — a phone charger might present hundreds of ohms while a space heater element is just a few ohms. There’s no single typical value; you generally need the device’s rated voltage and current from its label to work out its resistance.Why does lowering resistance increase current?
Because current equals voltage divided by resistance (I = V/R) at a fixed voltage. Lowering resistance lets more current flow for the same voltage, the same way a wider pipe lets more water through at the same pressure.Related Calculators
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