How an Ohm's Law Calculator Works
Ohm's Law is the foundation of electrical circuit analysis, linking voltage (V), current (I), and resistance (R). This calculator lets you choose which quantity to solve for, then enter any two of the remaining known values. It computes the answer and also reports power (P), so you get a complete picture of the circuit.
Voltage is measured in volts, current in amperes, resistance in ohms, and power in watts. Because the four quantities are interrelated, knowing any two lets you derive the other two.
The Core Equations
- V = I × R (voltage from current and resistance)
- P = V × I (power from voltage and current)
- P = I² × R (power from current and resistance)
- P = V² / R (power from voltage and resistance)
Using Ohm's Law in Practice
Ohm's Law is used everywhere from sizing resistors to checking whether a wire can safely carry a load. Understanding the relationships helps you design and troubleshoot circuits confidently.
- Increasing resistance reduces current for a fixed voltage.
- Power dissipation rises with the square of current, which is why thick wires are used for high-current loads.
- A short circuit has near-zero resistance, causing current and power to spike dangerously.
- LEDs and other components need a series resistor sized with Ohm's Law to limit current.
Frequently Asked Questions
What are the units in Ohm's Law?
Voltage is measured in volts (V), current in amperes or amps (A), resistance in ohms (Ω), and power in watts (W). This calculator expects values in these base SI units.
Why can't resistance or current be zero in some cases?
When solving for current you divide by resistance, and when solving for resistance you divide by current. Division by zero is undefined, so those inputs cannot be zero. Physically, zero resistance represents a short circuit and zero current means no flow at all.
How is power related to Ohm's Law?
Power is the rate at which electrical energy is used and equals voltage times current (P = VI). By substituting Ohm's Law you can also express power as I²R or V²/R, which is useful when you only know two of the variables.
