Energy and Power Conversion
Energy and power measurements quantify the capacity to perform work and the rate at which work is done. These measurements are essential in physics, engineering, and daily activities such as electricity consumption and fuel usage. The metric system uses joules and watts as base units, while imperial units include British thermal units and horsepower. Understanding both systems aids in global scientific communication and practical energy management.
Joules (J)
Kilojoules (kJ)
Megajoules (MJ)
Gigajoules (GJ)
Calories (cal)
Kilocalories (kcal)
Watt Hours (Wh)
Kilowatt Hours (kWh)
Megawatt Hours (MWh)
Electron Volts (eV)
British Thermal Units (BTU)
Therms (thm)
Foot-Pounds (ft⋅lbf)
Ergs (erg)
Watts (W)
Kilowatts (kW)
Megawatts (MW)
Gigawatts (GW)
Horsepower (hp)
Metric Horsepower (PS)
Foot-Pounds per Minute (ft⋅lbf/min)
Foot-Pounds per Second (ft⋅lbf/s)
BTU per Hour (BTU/h)
BTU per Minute (BTU/min)
Tons of Refrigeration (TR)
Milliwatts (mW)
Microwatts (µW)
Nanowatts (nW)
Terawatts (TW)
Petajoules (PJ)
Exajoules (EJ)
Calories (Nutritional) (Cal)
Tons of TNT (tTNT)
Kilotons of TNT (ktTNT)
Megatons of TNT (MtTNT)
Barrels of Oil Equivalent (BOE)
Unit Descriptions
- Joules
- The joule (J) is the SI unit of energy, defined as one newton meter of work.
- Kilojoules
- A kilojoule (kJ) equals 1,000 joules and measures moderate quantities of energy.
- Megajoules
- One megajoule (MJ) equals one million joules, used for larger energy amounts.
- Gigajoules
- A gigajoule (GJ) equals one billion joules, common in industrial energy assessments.
- Calories
- The calorie (cal) measures energy mainly in chemistry and food science, equal to 4.184 joules.
- Kilocalories
- A kilocalorie (kcal), often called a 'Calorie' in nutrition, equals 1,000 calories or 4,184 joules.
- Watt Hours
- A watt-hour (Wh) measures energy as one watt of power applied for one hour.
- Kilowatt Hours
- A kilowatt-hour (kWh) equals 1,000 watt-hours and is standard for electrical energy billing.
- Megawatt Hours
- One megawatt-hour (MWh) equals one million watt-hours, used for large-scale energy production.
- Electron Volts
- An electron-volt (eV) is the energy gained by an electron moving through one volt, equal to 1.602×10⁻¹⁹ joules.
- British Thermal Units
- The British thermal unit (BTU) measures heat energy, defined as the heat to raise one pound of water by one degree Fahrenheit.
- Therms
- A therm equals 100,000 BTUs and measures natural gas energy content.
- Foot-Pounds
- A foot-pound (ft·lb) measures energy as work done by a one-pound force over one foot distance.
- Ergs
- The erg is a small unit of energy in the CGS system, equal to 10⁻⁷ joules.
- Watts
- The watt (W) is the SI unit of power, representing one joule per second.
- Kilowatts
- A kilowatt (kW) equals 1,000 watts, commonly used for electric power ratings.
- Megawatts
- A megawatt (MW) equals one million watts, typical for power plant capacity.
- Gigawatts
- A gigawatt (GW) equals one billion watts, measuring large-scale power generation.
- Horsepower
- Mechanical horsepower (hp) equals approximately 745.7 watts, used for engine power.
- Metric Horsepower
- Metric horsepower equals 735.5 watts, used mainly in Europe for engine ratings.
- Foot-Pounds per Minute
- This unit measures power as foot-pounds of work done per minute.
- Foot-Pounds per Second
- Foot-pounds per second measure power as work done in foot-pounds each second.
- BTU per Hour
- BTUs per hour measure heat transfer rate, often for heating systems.
- BTU per Minute
- BTUs per minute measure a higher heat transfer rate than per hour.
- Tons of Refrigeration
- A ton of refrigeration equals 12,000 BTUs per hour, representing cooling capacity.
- Milliwatts
- A milliwatt (mW) equals one-thousandth of a watt, used for low-power devices.
- Microwatts
- A microwatt (µW) equals one-millionth of a watt, used in sensitive electronics.
- Nanowatts
- A nanowatt (nW) equals one-billionth of a watt, measuring extremely low power.
- Terawatts
- A terawatt (TW) equals one trillion watts, used for global energy consumption scales.
- Petajoules
- A petajoule (PJ) equals 10¹⁵ joules, used in large energy resource assessments.
- Exajoules
- An exajoule (EJ) equals 10¹⁸ joules, measuring national or global energy quantities.
- Calories (Nutritional)
- Nutritional calories equal kilocalories, quantifying food energy intake.
- Tons of TNT
- A ton of TNT equals 4.184 gigajoules, used to express explosive energy.
- Kilotons of TNT
- A kiloton of TNT equals 1,000 tons of TNT, used for bomb yield estimates.
- Megatons of TNT
- A megaton of TNT equals one million tons of TNT, used for nuclear explosion energy.
- Barrels of Oil Equivalent
- Barrels of oil equivalent (BOE) standardize energy amounts based on one barrel of crude oil.
FAQ
What is the difference between energy and power?
Energy measures the total work done or heat transferred, expressed in joules or calories. Power measures the rate of energy transfer or work per unit time, expressed in watts or horsepower. Essentially, power is energy divided by time.
How do joules relate to calories?
One calorie equals approximately 4.184 joules. Calories often measure food energy, while joules are the SI unit for all energy forms. This conversion allows comparison between nutritional and physical energy units.
What is a kilowatt-hour used for?
A kilowatt-hour (kWh) measures electrical energy consumption over time. Utilities charge customers based on kWh usage. One kWh equals 3.6 million joules.
Why are British thermal units (BTUs) important?
BTUs quantify heat energy in the imperial system, commonly used in heating and cooling industries. One BTU equals about 1055 joules. They help specify energy in HVAC and fuel systems.
How does horsepower compare to watts?
One metric horsepower equals 735.5 watts, while one mechanical horsepower equals approximately 745.7 watts. Horsepower measures power mainly in mechanical contexts like engines. Watts are the SI unit for power.
What are electron-volts used for?
Electron-volts (eV) measure very small energy scales, typically in atomic and particle physics. One eV equals 1.602×10⁻¹⁹ joules. They quantify energy changes at the quantum level.
What does tons of refrigeration measure?
Tons of refrigeration quantify the cooling capacity of air conditioning systems. One ton equals 12,000 BTUs per hour. This unit helps size cooling equipment accurately.
How is power expressed in units like milliwatts and gigawatts?
Milliwatts measure very small power levels (1/1000 watt), useful in electronics. Gigawatts measure very large power outputs, such as electrical grids or power plants. These units scale power to practical magnitudes.
What is the significance of barrels of oil equivalent?
Barrels of oil equivalent (BOE) convert diverse energy sources to a single unit based on the energy in one barrel of crude oil. This unit standardizes comparisons of energy production or consumption across fuels.
How do therms relate to energy usage?
Therms measure natural gas energy content, commonly in the US and UK. One therm equals 100,000 BTUs or about 105.5 megajoules. This unit facilitates billing and energy accounting.