Power Calculator

Calculate electrical power, voltage, current, and resistance. Free online power calculator for electrical engineering.

What is Power Calculator?

A power calculator helps you understand the relationship between electrical power, voltage, current, and resistance. Power, measured in watts, represents the rate at which energy is consumed or produced. Whether you're sizing a generator, calculating electricity costs, or designing an electrical circuit, understanding power calculations is essential.

Electrical power is one of the most practical measurements in daily life. Your electricity bill is based on kilowatt-hours (kWh), appliance ratings are in watts, and circuit breakers are sized based on the current (amperes) they can safely handle. This calculator helps you determine any electrical parameter when you know the others, making it invaluable for both DIY projects and professional electrical work.

Formula

P = V × I (Power = Voltage × Current)

P = I² × R (Power = Current² × Resistance)

P = V² / R (Power = Voltage² ÷ Resistance)

Where: P = Power (watts), V = Voltage (volts), I = Current (amperes), R = Resistance (ohms)

How to Calculate

Select which value you want to calculate (power, voltage, current, or resistance).
Enter the known values.
The calculator computes the unknown value.
View all related electrical parameters.
Use the results for circuit design or energy cost estimation.

Example

A 100-watt light bulb connected to a 120V circuit draws I = P/V = 100/120 = 0.833 amperes. Its resistance is R = V²/P = 120²/100 = 144 ohms. Running this bulb for 10 hours consumes 1 kWh of energy.

Key Benefits

Electrical mechanical power multiple formulas
Convert watt hp BTU kilowatt seamlessly
Understand power current voltage resistance
Determine consumption efficiency

Common Mistakes to Avoid

Real power watts vs apparent VA AC
Forgetting power factor in AC
Horsepower watts without conversion

Pro Tips

1 hp = 746 watts for conversion
Account power factor real vs apparent
Use P = F*v for mechanical power

Key Terms Explained

Watt W: SI power joule per second
Horsepower: 550 ft-lb per second
Efficiency: Output over input percentage
Power Factor: Real vs apparent power ratio

When to Use This Calculator

Sizing generators transformers supplies
Calculating appliance energy costs
Comparing engine motor power output

Common Use Cases

Calculating electricity consumption and costs for appliances
Sizing circuit breakers and wiring for electrical installations
Determining generator capacity for backup power systems
Analyzing power requirements for electronic projects

Frequently Asked Questions

What's the difference between watts and kilowatt-hours?

Watts measure power (rate of energy use). Kilowatt-hours measure energy consumed over time. A 1,000-watt appliance running for 1 hour uses 1 kWh of energy.

How do I calculate electricity cost?

Multiply the appliance's power in kW by hours of use, then by your electricity rate per kWh. Example: A 1.5 kW heater running 8 hours at $0.12/kWh costs 1.5 × 8 × 0.12 = $1.44.

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