Ohm's Law Calculator
Enter any two of voltage, current, resistance or power and this calculator finds the remaining two using Ohm's law (V = I x R) and the power equation (P = V x I).
How to use the Ohm's law calculator
- Enter exactly two known values, for example voltage and resistance.
- Leave the two unknown fields blank.
- Read off the calculated current, power or whichever values were missing.
Examples
Voltage and resistance
V = 12 V, R = 4 ohm
I = 3 A, P = 36 W
Current and power
I = 2 A, P = 24 W
V = 12 V, R = 6 ohm
Frequently asked questions
What is Ohm's law?
Ohm's law states that voltage equals current times resistance (V = I x R). Combined with the power law P = V x I, it links all four quantities.
How many values do I need to enter?
Exactly two. From any two of voltage, current, resistance and power the other two are fully determined.
What units does it use?
Volts for voltage, amperes for current, ohms for resistance and watts for power. Convert milliamps to amps by dividing by 1000.
Which formulas are used?
V = I x R, P = V x I, P = I^2 x R and P = V^2 / R. The calculator picks the right pair for the values you supply.
Why can't resistance be zero with voltage?
Dividing voltage by zero resistance gives infinite current, which is not physically meaningful, so that combination is rejected.
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