# Electrical Power Calculator (P = IV)

Calculate electrical power using P = IV, P = I²R, or P = V²/R. Find power in watts from voltage, current, and resistance.

## What this calculates

Electrical power is the rate at which electrical energy is converted into other forms such as heat, light, or motion. This calculator uses three equivalent formulas: P = IV (power from voltage and current), P = I²R (power from current and resistance), and P = V²/R (power from voltage and resistance). It also estimates daily energy cost.

## Inputs

- **Voltage (V)** (V) — min 0
- **Current (I)** (A) — min 0
- **Resistance (R)** (Ω) — min 0

## Outputs

- **Power** (W) — Electrical power in Watts
- **Power** (kW) — Power in kilowatts
- **Energy per Hour** (Wh) — Energy consumed per hour
- **Daily Cost (at $0.12/kWh)** — formatted as currency — Approximate daily electricity cost

## Frequently Asked Questions

**Q: What is electrical power?**

A: Electrical power is the rate at which electrical energy is transferred in a circuit, measured in Watts (W). One Watt equals one Joule per second. It is calculated as P = IV (voltage times current). A 100 W light bulb converts 100 joules of electrical energy into light and heat every second.

**Q: What is the relationship between watts, volts, and amps?**

A: Power (watts) = Voltage (volts) × Current (amps). If you know any two of these three quantities, you can calculate the third. For example, a device drawing 2 A from a 120 V outlet uses 240 W of power. This is the most fundamental equation in electrical engineering.

**Q: How do I calculate electricity cost?**

A: Electricity is billed in kilowatt-hours (kWh). Multiply the power in kilowatts by the number of hours of use, then multiply by your rate per kWh. For example, a 100 W device running 24 hours uses 2.4 kWh. At $0.12/kWh, that costs about $0.29 per day or $8.64 per month.

**Q: Why does P = I²R give the same result as P = V²/R?**

A: Both are derived from P = IV combined with Ohm's Law (V = IR). Substituting V = IR into P = IV gives P = I²R. Substituting I = V/R into P = IV gives P = V²/R. All three formulas are equivalent and give the same power, just using different combinations of the known quantities.

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Source: https://vastcalc.com/calculators/physics/electrical-power
Category: Physics
Last updated: 2026-04-21