What is Ohm's Law?
Ohm's Law describes the relationship between voltage, current and resistance in an electrical circuit. Voltage is measured in volts, current in amperes and resistance in ohms.
How to calculate current
When voltage and resistance are known, divide voltage by resistance to calculate current.
How to calculate resistance
When voltage and current are known, divide voltage by current to calculate resistance.
Worked example
If a circuit has 12 volts across a resistance of 6 ohms, the current is 2 amperes because 12 divided by 6 equals 2.
Understanding the three quantities
- Voltage represents electrical potential difference.
- Current describes the rate of electric charge flow.
- Resistance describes opposition to current flow.
- Changing one quantity can affect the others depending on the circuit.
Ohm's Law and electrical power
Ohm's Law is often used together with the electrical power relationship. When voltage and current are known, power can be calculated in watts.
Formula calculations do not replace electrical design requirements, equipment ratings or applicable electrical codes. Work on mains-voltage systems should be performed by appropriately qualified people.