Ohms Law Power Calculator

What Is an Ohm's Law Power Calculator?

An Ohm's law power calculator finds electrical power dissipated or delivered in a circuit. Power tells you how much energy per second flows through a load, which matters for heat sinking, wire sizing, and energy billing.

Three Power Formulas

Electrical power connects voltage, current, and resistance in three equivalent forms:

$$P = V \times I$$ $$P = I^2 \times R$$ $$P = \frac{V^2}{R}$$

Use the first when you know voltage and current, the second when you have current and resistance, and the third when voltage and resistance are given.

Choosing the Right Formula

A 120 V outlet feeding 2.5 A delivers 300 W. The same power appears as I²R when you measure current through a known resistor, or as V²/R when you know the supply voltage and load resistance. Pick the form that matches your measured values.

Frequently Asked Questions

What unit is electrical power measured in?

Power is measured in watts (W). One watt equals one joule per second. Larger loads use kilowatts (kW).

Why does P = I²R matter for wire heating?

Current squared means doubling current quadruples heat in a fixed resistance. That is why undersized wires get hot long before voltage drop becomes obvious.

Is power the same as energy?

No. Power is the rate of energy use (watts). Energy is power multiplied by time, measured in watt-hours or joules.

Can I use these formulas for AC?

For resistive AC loads, yes. For motors and other reactive loads, use RMS voltage and current, and account for power factor separately.

How do I convert watts to horsepower?

Divide watts by 746 to get mechanical horsepower. Our HP to Amps calculator works in the opposite direction for motor sizing.

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What Is an Ohm's Law Power Calculator?

Three Power Formulas

Choosing the Right Formula

Frequently Asked Questions

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