Power to Energy Converter
Our free thermal & energy converter handles power energy conversions. See tables, ratios, and examples for quick reference.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Power to Energy Converter
Calculator
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Formula: Energy = Power x Time | E (J) = P (W) x t (s) | E (kWh) = P (kW) x t (h)
Worked example โ 12 kWh = 43.2 MJ = 10,325 kcal, costing $1.44
Formula
Energy = Power x Time | E (J) = P (W) x t (s) | E (kWh) = P (kW) x t (h)
Energy is the product of power and time. In SI units, 1 watt for 1 second equals 1 joule. For electricity billing, the kilowatt-hour is standard: 1 kW for 1 hour = 1 kWh = 3,600,000 joules. This converter handles the unit conversions automatically, letting you input power in any unit and time in any duration.
Worked Examples
Example 1: Home Appliance Energy Use
Problem:A 1,500 W space heater runs for 8 hours. How much energy does it consume?
Solution:Energy = Power x Time Energy = 1,500 W x 8 h = 12,000 Wh = 12 kWh In joules: 1,500 W x 28,800 s = 43,200,000 J = 43.2 MJ Cost at $0.12/kWh: 12 x $0.12 = $1.44
Result:12 kWh = 43.2 MJ = 10,325 kcal, costing $1.44
Example 2: Industrial Motor Energy
Problem:A 10 HP motor runs continuously for 24 hours. Calculate total energy in kWh.
Solution:Convert HP to kW: 10 x 0.7457 = 7.457 kW Energy = 7.457 kW x 24 h = 178.97 kWh In MJ: 178.97 x 3.6 = 644.3 MJ Cost at $0.12/kWh: 178.97 x $0.12 = $21.48
Result:10 HP for 24 hours = 178.97 kWh = 644.3 MJ
Frequently Asked Questions
How do you calculate energy from power and time?
Energy equals power multiplied by time. In SI units, energy (joules) = power (watts) x time (seconds). For practical purposes, electricity is measured in kilowatt-hours: energy (kWh) = power (kW) x time (hours). For example, a 100-watt bulb running for 10 hours uses 100 x 10 = 1,000 Wh = 1 kWh of energy. This relationship is fundamental to all energy calculations and electricity billing.
What is the difference between power and energy?
Power is the rate at which energy is transferred or converted, measured in watts (joules per second). Energy is the total amount of work done or heat transferred, measured in joules or kilowatt-hours. Think of power as speed and energy as distance. A 1,000-watt microwave uses energy faster than a 100-watt bulb, but total energy consumed depends on how long each runs. Power is instantaneous; energy is cumulative over time.
How do I calculate my electricity cost from power usage?
First calculate energy in kWh: multiply the device power in kW by hours of use. Then multiply by your electricity rate (cost per kWh). For example, a 1,500 W space heater running 8 hours: 1.5 kW x 8 h = 12 kWh. At $0.12/kWh: 12 x $0.12 = $1.44 per day. To find monthly cost, multiply daily cost by 30 days: $1.44 x 30 = $43.20 per month.
How do I convert horsepower to energy?
First convert horsepower to watts: 1 mechanical horsepower = 745.7 watts. Then multiply by time in seconds to get joules, or by time in hours to get watt-hours. For example, a 5 HP motor running for 2 hours: 5 x 745.7 = 3,728.5 W = 3.7285 kW. Energy = 3.7285 kW x 2 h = 7.457 kWh. This is useful for calculating energy costs of motors, pumps, and other mechanical equipment.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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