Electrical Power Calculator for V, I and R

Electrical power is one of the core quantities in circuit analysis because it tells you how quickly electrical energy is being transferred or dissipated. In the simplest direct-current relationships, power can be written three equivalent ways: P = V·I, P = I²R, and P = V²/R. Which version you use depends on which circuit values you already know. This calculator is organized around that exact decision, letting you select voltage plus current, voltage plus resistance, or current plus resistance as your starting pair. If you know voltage and current, the power equation is direct: multiply the two to get watts. The same pair also lets you solve resistance from R = V/I. This is common when checking a power supply, measuring a load, or estimating the equivalent resistance of a component drawing a known current from a known voltage source. If you know voltage and resistance, the more convenient form is P = V²/R. That avoids having to calculate current separately first, although the calculator also derives current with I = V/R so you can see the full picture. This mode is useful for resistor sizing, heater calculations, and quick checks on how much current a fixed supply will push through a known resistance. If you know current and resistance, the natural form is P = I²R and the associated voltage is V = IR. This case appears often when you know the load current and conductor or resistor value, such as in cable heating estimates, shunt calculations, or actuator drive checks. Because power scales with current squared, even modest increases in current can produce much larger heat dissipation. These formulas assume a simple resistive relationship and steady values, which is ideal for introductory electronics, DC circuits, and many fast engineering approximations. Real AC systems, reactive components, switching waveforms, and nonlinear devices may require RMS values, power factor corrections, or more advanced analysis. Even so, the three identities used here remain the fastest and most familiar way to verify basic electrical power behavior.