Electrical Power Calculator
Plan your electrical projects with confidence. Calculate the wattage draw of your appliances or the amperage required for your circuits using our precise 3-way power solver.
Result
Watts
Joule's Law
Electrical power (P) is the rate at which electrical energy is transferred by an electric circuit. It is measured in Watts (W).
P = V × I
A typical 13A UK plug at 240V can handle up to 3,120W.
Power is also related to resistance via $P = I²R$ or $P = V²/R$.
Appliance Guide
Understanding Wattage
Electrical power is the rate at which work is done or energy is transformed in an electrical circuit. It is measured in Watts (W), named after James Watt.
The relationship between power (P), voltage (V), and current (I) is defined by Joule's Law: $P = V \times I$. This means that for a fixed voltage, increasing the current increases the power consumed.
Safety & Planning
Overload Prevention: Ensuring total wattage doesn't exceed fuse ratings.
Energy Efficiency: Identifying high-draw appliances to save on bills.
Solar Design: Matching panel output to inverter capacity.
UPS Sizing: Choosing the right backup battery for your hardware.
Frequently Asked Questions
What is the difference between Watts and VA?
Watts represent 'Real Power' (work done), while VA (Volt-Amperes) represent 'Apparent Power'. In DC circuits they are equal, but in AC circuits, the difference depends on the 'Power Factor'.
How many Watts are in a Kilowatt?
There are 1,000 Watts in 1 Kilowatt (kW). Electrical bills are typically charged per Kilowatt-hour (kWh).
Why do some appliances use more power?
Appliances that generate heat (kettles, showers, heaters) require significant energy to overcome the resistance of heating elements, leading to high wattage draw.
Can I calculate power with resistance?
Yes. By combining Ohm's Law and Joule's Law, you can use $P = I²R$ (useful for cables) or $P = V²/R$ (useful for fixed-voltage appliances).