Ohm's Law Calculator
Ohm's law links voltage, current and resistance. Enter the voltage and the current, and this shows the resistance and the power for a simple circuit.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Resistance is voltage divided by current. Power in watts is voltage times current.
These formulas assume a simple circuit with one resistance. Real devices can behave differently, so use this for learning and rough checks.
Worked example
At 12 volts and 2 amps, the resistance is 6 ohms and the power is 24 watts.
Questions
What if the current is zero?
Resistance cannot be worked out by dividing by zero, so the calculator needs a current above zero.
Is this enough to size a wire or a breaker?
No. This does not cover wire size, breaker rules or local code. A licensed electrician can help with those.
Does it work for AC circuits?
The simple form is for direct current or purely resistive loads. AC circuits with motors or other parts need more.
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