Electrical Power Lab
Master the Power Formulas ($P=VI$) and Calculate Energy Costs.
Universal Power Solver
Enter ANY TWO values. The calculator will find the other two automatically using $P=VI$ and $V=IR$.
Variable Cheatsheet
| Symbol | Quantity | SI Unit | Notes |
|---|---|---|---|
| P | Electrical Power | Watts (W) | Rate of energy usage (1 kW = 1000 W) |
| V | Voltage | Volts (V) | Pushing force (Potential Difference) |
| I | Current | Amperes (A) | Flow of electrons per second |
| R | Resistance | Ohms (Ω) | Opposes the flow of current |
| E | Energy | kWh / Joules | Total usage (Power × Time) |
Powering the World.
From your smartphone to huge city grids, Power ($P$) defines how fast energy is moved. Use the calculator above to estimate your real-world energy costs.
The Workhorse (P=VI)
The universal formula. Used for batteries, solar panels, and motors. If you know Volts and Amps, you know Watts.
The Heater (P=I²R)
Calculates Heat Loss. Shows that doubling current ($I$) creates 4x the heat. Vital for choosing wire thickness.
The Load (P=V²/R)
Best for devices in Parallel (like your home). Explains why a lower resistance bulb shines brighter on mains voltage.
Save Money: The kWh Truth
Most people confuse Power (kW) with Energy (kWh). You afford a 2000W kettle easily because you run it for 2 minutes. You might struggle with a 2000W Heater because you run it for 8 hours.
Frequently Asked Questions
What is the formula for Electrical Power?
The primary formula is $P = V \times I$ (Voltage × Current). Variations include $P = I^2 R$ (Current squared × Resistance) and $P = V^2 / R$ (Voltage squared / Resistance).
How do I calculate my Electricity Bill?
First, find the energy used in kWh: (Watts × Hours) / 1000. Then multiply by your rate: kWh × Rate ($/kWh). Example: A 1000W heater for 5 hours = 5 kWh. At $0.15/kWh, it costs $0.75.
Why is P = I²R called Power Loss?
This formula often describes heat wasted in wires. Since wires have fixed Resistance ($R$), doubling the Current ($I$) quadruples the heat loss ($2^2 = 4$). This is why power lines use high voltage to keep current low.
What is the difference between Power (kW) and Energy (kWh)?
Power (kW) is the rate of using energy (like speed). Energy (kWh) is the total amount used (like distance). A 100kW car engine (Power) running for 1 hour uses 100kWh of Energy.
Does a charger unplugged use power?
Mostly no, or negligible. A charger not connected to a phone draws "Vampire Power" but it is usually less than 0.1 Watts, costing mere cents per year.
Is 220V better than 110V?
220V allows for thinner wires because it requires half the current to deliver the same power ($P=VI$). However, 110V is generally considered safer for accidental shocks.
How many Watts is 1 Horsepower?
1 Mechanical Horsepower (HP) is approximately 746 Watts. So a 1 HP motor uses about the same power as a microwave.
Why do light bulbs blow out?
When first turned on, the filament is cold and has LOW resistance. This causes a sudden surge of HIGH current ($I=V/R$), which can stress and snap the filament.
What is the unit of Electrical Consumption?
The Kilowatt-Hour (kWh). It represents using 1000 Watts for 1 Hour. Your electric meter counts these units.
Does higher voltage mean higher power?
Not necessarily. Power depends on BOTH Voltage and Current ($P=VI$). A taser has 50,000 Volts but tiny Current, so low Power. A car battery has 12 Volts but huge Current, so high Power.