Pick the value you want, fill in the other two, and see power at the same time.
How it works
Ohm's law says voltage equals current times resistance. Power is voltage times current.
Before you order
- Turn power off before you measure resistance on any circuit.
- A resistance that reads near zero often means a short.
- Power tells you how much heat a part must get rid of, so check the part's watt rating.
Common questions
Does this work for AC?
For resistive loads like heaters, yes. Motors and electronics add reactance and power factor, so treat the answer as an approximation.
Why does a small current drop matter?
Current squared drives heating in wires, so high-resistance connections run hot long before a breaker trips.