Ohm's Law Calculator

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across those points. It is expressed as V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. It applies to circuits with purely resistive elements under both DC and AC conditions.

You need to enter any two of the four values — Voltage (V), Current (I), Resistance (R), or Power (P) — and the calculator will solve for the remaining two. Make sure you leave the fields you want to calculate completely blank.

Electrical power is calculated using P = V × I, where P is power in watts, V is voltage in volts, and I is current in amperes. It can also be expressed as P = I² × R or P = V² / R depending on which values are known.

This calculator uses standard SI units: Volts (V) for voltage, Amperes (A) for current, Ohms (Ω) for resistance, and Watts (W) for power. If your values are in millivolts, milliamps, kilohms, or kilowatts, convert them to the base unit before entering.

Ohm's Law in its basic form (V = I × R) applies to purely resistive AC circuits. In circuits with capacitors or inductors, impedance replaces resistance and complex numbers are used. For simple resistive components like heating elements or resistors, the law holds under AC as well.

Voltage, current, and resistance are directly linked: if resistance stays constant, increasing voltage increases current proportionally. If voltage stays constant, increasing resistance decreases current. This relationship is the foundation of circuit design and electrical engineering.

Yes. Ohm's Law is commonly used to calculate safe operating conditions for vaping devices, battery-powered circuits, and DIY electronics. Enter your battery voltage and coil resistance to find the current draw and wattage output.

If you enter three or four values, the calculator will use the first valid pair it finds to compute the results. For best accuracy, enter only the two values you know and leave the others blank so the calculator can solve for them unambiguously.