The two relationships at work
Ohm’s law links three quantities in a circuit: voltage is the electrical pressure pushing charge, current is the rate of flow, and resistance is how much the conductor opposes that flow. They tie together as V = I × R, so any one can be found from the other two.
Power — the rate energy is delivered — adds a fourth quantity through P = V × I. Combining the two relationships means that knowing any two of voltage, current, resistance and power fixes the remaining two, which is exactly what this calculator does.
How to use it
Enter exactly two of the four fields and leave the others blank. The calculator detects which pair you gave and solves the rest with the appropriate rearrangement.
- Voltage and current are the most common pair from a multimeter reading.
- Resistance and power, or current and power, also work — the math handles every combination.
- Entering three or more values is ambiguous, so the tool asks for just two.
Watching the units
Results scale across a huge range, so prefixes matter. A milliamp is a thousandth of an amp and a kilohm is a thousand ohms; mixing them silently throws answers off by orders of magnitude. Convert everything to base units (volts, amps, ohms, watts) before entering values, then read the results in the same base units.
Where the simple law stops applying
These equations describe a steady direct-current (DC) circuit with a constant, linear resistance. They do not capture alternating-current effects like reactance and impedance, nor non-ohmic devices such as diodes and LEDs whose resistance changes with voltage. For AC analysis or semiconductors, more complete models are needed.
Formula
V = I·R; P = V·I