Ohm’s law formulas and quick examples
- Current: I = V ÷ R
- Voltage: V = I × R
- Resistance: R = V ÷ I
- Power: P = V × I
- 12 V ÷ 6 Ω = 2 A
- 12 V × 2 A = 24 W
Ohm’s Law Calculator
Calculate voltage, current, resistance and electrical power from any two known Ohm’s law quantities, with practical support for mV, V, kV, µA, mA, A, kA, mΩ, Ω, kΩ and MΩ inputs.
Example: voltage is 12 volts and resistance is 6 ohms. What are the current and power?
Calculated current 2 A 12 V ÷ 6 Ω = 2 A
Electrical power 24 W 12 V × 2 A = 24 W
Full solution V = 12 V · I = 2 A · R = 6 Ω · P = 24 W Results are shown in the base units volt, ampere, ohm and watt.
✓ Volt, ampere and ohm relationships are consistent with NIST-published SI unit definitions
How is it calculated?
Ohm’s law uses V = I × R. With voltage and resistance, I = V ÷ R; with voltage and current, R = V ÷ I; with current and resistance, V = I × R. Power is then calculated from P = V × I.This calculation runs in your browser. Your values are not sent to our server.
How it works
- Choose which two electrical quantities you already know: voltage and resistance, voltage and current, or current and resistance.
- Enter both values and choose their units. The calculator converts those inputs to volts, amperes and ohms before solving the relationship.
- Ohm’s law is V = I × R. Rearranging gives I = V ÷ R and R = V ÷ I.
- Electrical power is then calculated as P = V × I and displayed in watts.
- Example: with 12 V and 6 Ω, current is exactly 2 A and power is exactly 24 W.
- This calculator treats entered values as non-negative magnitudes for a simple resistive DC relationship; it is not a circuit-safety or wiring-design tool.
Formula and SI unit sources
FAQ
What is Ohm’s law?
Ohm’s law relates voltage, current and resistance using V = I × R.
How do I calculate current from voltage and resistance?
Divide voltage by resistance: I = V ÷ R. For example, 12 V ÷ 6 Ω = 2 A.
How do I calculate resistance from voltage and current?
Divide voltage by current: R = V ÷ I. For example, 12 V ÷ 2 A = 6 Ω.
How do I calculate voltage from current and resistance?
Multiply current by resistance: V = I × R. For example, 2 A × 6 Ω = 12 V.
Does the calculator also calculate electrical power?
Yes. Once voltage and current are known, it calculates power with P = V × I.
Is this the same as the resistance unit converter?
No. The resistance converter changes units such as mΩ, Ω and kΩ. This calculator solves the electrical relationship between voltage, current and resistance.