How to Use Watt Calculator
The Watt Calculator supports three common power formulas. Select the one that matches the values you already know:
- P = V × I — Select this formula, enter voltage in volts (V) and current in amps (A). The Watt Calculator instantly displays power in watts.
- P = I² × R — Select this formula, enter current (A) and resistance in ohms (Ω). The Watt Calculator computes P = I squared times R.
- P = V² / R — Select this formula, enter voltage (V) and resistance (Ω). The Watt Calculator divides the squared voltage by resistance to find power.
The result is shown in both watts (W) and kilowatts (kW), along with the formula used, so you can always verify the calculation at a glance.
Formula & Theory — Watt Calculator
The Watt Calculator is grounded in Ohm's Law and the power law of electrical circuits. All three formulas are algebraically equivalent — they derive from the same two base equations (V = I × R and P = V × I):
Formula 1: P = V × I (Voltage × Current)
Formula 2: P = I² × R (Current squared × Resistance)
Formula 3: P = V² / R (Voltage squared ÷ Resistance)
| Symbol | Meaning | Unit |
|---|---|---|
| P | Electric power | W (Watts) |
| V | Voltage | V (Volts) |
| I | Current | A (Amps) |
| R | Resistance | Ω (Ohms) |
Unit Conversion
The Watt Calculator automatically converts watts to kilowatts: 1 kW = 1,000 W. For large installations — motors, HVAC systems, industrial equipment — the kilowatt reading is typically more practical.
Use Cases for Watt Calculator
The Watt Calculator is a versatile tool for students, engineers, and hobbyists alike:
- Circuit design — Verify that components are within their power ratings before building. Use the Watt Calculator with P = I² × R to find the power dissipated across a resistor.
- Home appliance analysis — Check the power draw of any device that lists its operating voltage and current on the nameplate. The Watt Calculator gives you the wattage instantly.
- Electronics prototyping — When designing PCBs or selecting MOSFETs and transistors, use the Watt Calculator to confirm that power dissipation stays within safe limits.
- Electrical education — The Watt Calculator is a great companion tool for students learning Ohm's Law, helping visualize how voltage, current, and resistance interact to produce power.
- Energy audits — Combine the Watt Calculator with a Power Consumption Calculator to build a complete picture of device-level energy use in a home or office.
With three formulas on a single page, the Watt Calculator eliminates the need to rearrange equations manually and makes power calculations fast and error-free.