Ohm's Law Calculator
Enter any two values and instantly calculate the other two - voltage (V), current (I), resistance (R), and power (P). Covers all of the Ohm's law and power relationships for DC and resistive circuits.
Enter any two values - the other two are calculated.
Voltage
12V
Current
2A
Resistance
6Ω
Power
24W
Key relationships
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The Ohm's law relationships
Ohm's law links the four fundamental quantities of an electrical circuit. Knowing any two lets you derive the other two:
- V = I × R - voltage equals current times resistance.
- I = V ÷ R - current equals voltage divided by resistance.
- R = V ÷ I - resistance equals voltage divided by current.
- P = V × I - power equals voltage times current.
Worked example
A heating element draws 2 A from a 12 V supply. What is its resistance and power?
- R = V ÷ I = 12 ÷ 2 = 6 Ω
- P = V × I = 12 × 2 = 24 W
Frequently Asked Questions
- What is Ohm's law?
- Ohm's law states that the current through a conductor is directly proportional to the voltage and inversely proportional to the resistance: I = V ÷ R. Rearranged, V = I × R and R = V ÷ I.
- How do I calculate power from Ohm's law?
- Power can be found three ways: P = V × I, P = I² × R, or P = V² ÷ R. The calculator above uses whichever pair of values you enter.
- Does Ohm's law work for AC circuits?
- Ohm's law applies directly to DC and purely resistive AC circuits. For AC with inductance or capacitance, resistance is replaced by impedance (Z) and a power factor is applied to the power calculation.
- What are the units in Ohm's law?
- Voltage is measured in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W).
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