Calculate ohm's law

Solve voltage, current, resistance, and power at one linear resistive operating point.

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ToolOhm's Law Calculator
Input
Output
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Preview

How it works

Ohm’s law V = IR is rearranged to solve the missing quantity. Power is derived as P = VI or the equivalent I²R and V²/R forms.

  • The model assumes linear resistance.
  • Reactive impedance and thermal change are excluded.

Worked example

12V across a 4 ohm load
Voltage and resistance given, current and power worked out
Input
											Voltage volts: 12
Resistance ohms: 4
Output
												Voltage volts: 12
Current amps: 3
Resistance ohms: 4
Power watts: 36

When to use this

Circuit lessons solve resistor current, technicians estimate dissipation, and prototypes check supply and load values.

Edge cases

  • Zero resistance makes V ÷ R undefined.
  • Negative resistance can describe an active device but not a passive resistor.
  • LEDs and motors are not ohmic across their whole curves.