Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law (V=IR). Enter any two values to instantly compute the remaining electrical quantities.
Type into any 2 fields. The calculator will automatically lock those as your inputs and solve the other 2 fields.
Applying a standard 50% safety margin, the resistor should be rated for at least 9 W.
High power dissipation! Ensure adequate ventilation or use a chassis-mount power resistor.
R = V / I
P = V * I
About Ohm's Law Calculator
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = IR. Combined with the power formula P = VI, you can derive any of the four electrical quantities given any two known values. This calculator supports all six combinations of two known values and displays results with appropriate SI prefixes (milli, kilo, mega, etc.) for readability. Essential for electronics hobbyists, electrical engineers, and students.
Private & free — this tool runs entirely in your browser.