Ohm's Law Calculator
Solve for voltage, current, resistance, or power — enter any two values and get the remaining quantities.
How this is calculated
Ohm's law, V = IR, relates voltage, current and resistance with one equation — rearranged as I = V/R or R = V/I depending on which value you leave blank. Power dissipated is then calculated as P = IV using the resolved voltage and current.
Power extends Ohm's law to answer a different question: not just how voltage, current, and resistance relate, but how much energy per second is actually being dissipated (usually as heat) by a component. Using this calculator's defaults — 12V across a circuit drawing 2A — resistance is R = V/I = 12/2 = 6Ω, and power dissipated is P = V × I = 12 × 2 = 24W. That 24W is the rate at which the resistor converts electrical energy into heat — over one hour of continuous operation, that's 24 watt-hours of energy, the same unit electricity bills are measured in. For the full set of power formulas (P = IV, P = I²R, P = V²/R) and how to solve them from any two known values, see the Electrical Power calculator, and for the analogous force/mass/acceleration relationship in mechanics, see the Force / Mass / Acceleration calculator.
Frequently asked questions
- What is Ohm's law?
- Ohm's law states that the voltage across a conductor is proportional to the current flowing through it, with resistance as the constant of proportionality: V = IR. It's the fundamental relationship for basic circuit analysis.
- How is power related to Ohm's law?
- Power (P, in watts) is voltage times current: P = IV. Combined with V = IR, you get two more useful forms: P = I²R and P = V²/R — see the Electrical Power Calculator for solving those directly.
- What units does this use?
- Voltage in volts (V), current in amps (A), resistance in ohms (Ω), and power in watts (W) — standard SI electrical units.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.
- What is the difference between voltage, current, and resistance?
- Voltage is the electrical potential difference that drives current through a circuit — analogous to water pressure. Current is the actual flow of electric charge — analogous to water flow rate. Resistance opposes that flow — analogous to a narrow pipe restricting water flow. Ohm's law ties all three together in one equation.
- What is the SI unit of resistance?
- The ohm (Ω), named after physicist Georg Ohm. One ohm is defined as the resistance that produces a current of one amp when one volt is applied across it.
- How does Ohm's law apply to real circuits?
- Ohm's law applies precisely to purely resistive components (like resistors and simple heating elements) at a given temperature. Many real components — diodes, transistors, and resistors that heat up significantly under load — don't follow a strictly linear voltage-current relationship, so Ohm's law is an accurate model for ideal resistive elements but an approximation for more complex real-world components.