Energy Converter Calculator
Convert between all common energy units. From joules and calories for science and nutrition to kilowatt-hours for electricity bills and BTU for heating, this tool handles every energy conversion you need.
Understanding Energy Units
Energy is the capacity to do work, and humans have developed many units to measure it. The joule, the SI standard, is defined as the work done when a force of one newton moves an object one meter. Most scientific work uses joules, kilojoules, or megajoules depending on the scale of the phenomenon being studied.
Calories have a dual life in science and nutrition. In chemistry, a calorie is a tiny unit: the energy to warm one gram of water by one degree Celsius. In nutrition, a Calorie (capital C) is actually a kilocalorie, 1,000 times larger. This naming convention confuses millions of people reading food labels, but changing it now would cause even more confusion.
Electricity is measured in kilowatt-hours, a unit that combines power and time. One kWh is the energy delivered by 1,000 watts flowing for one hour. Your electric bill totals up kWh consumed over the billing period. Understanding this unit helps you estimate costs when shopping for appliances or considering solar panel installations.
Energy in Heating and Cooling
The BTU dominates heating and cooling specifications in the United States. Air conditioner capacity is rated in BTU per hour, with a typical window unit providing 5,000 to 12,000 BTU/h. Furnaces range from 40,000 to over 100,000 BTU/h. Converting between BTU and metric units is essential when comparing equipment from different manufacturers worldwide.
Natural gas is often billed in therms, where one therm equals 100,000 BTU or about 105.5 megajoules. A typical US household uses 50 to 100 therms per month during winter for heating. Understanding these energy units helps homeowners compare heating costs between gas, electric, and heat pump systems on an equal basis.
Heat pump efficiency is measured by the coefficient of performance, which compares energy output to electrical input. A heat pump with a COP of 3 delivers 3 kWh of heat for every 1 kWh of electricity consumed. Converting between BTU and kWh lets you compare heat pump specifications against traditional furnace ratings to determine which system saves more money.
Energy in Physics and Chemistry
Particle physics uses the electronvolt and its multiples: keV, MeV, GeV, and TeV. The Large Hadron Collider accelerates protons to energies of 6.5 TeV, which sounds enormous but is actually about the kinetic energy of a flying mosquito. The difference is that all this energy is concentrated in a single proton, making collisions extraordinarily energetic at the subatomic scale.
Chemical reactions release or absorb energy measured in kilojoules per mole. Burning one mole of methane releases about 890 kJ. Photosynthesis absorbs about 2,870 kJ per mole of glucose produced. These values are tabulated in reference books and allow chemists to predict whether a reaction will release heat or require energy input.
Nuclear reactions involve energies millions of times larger than chemical reactions. The fission of one uranium-235 atom releases about 200 MeV, roughly 3.2 x 10^-11 joules. While tiny per atom, a kilogram of uranium contains billions of trillions of atoms, giving nuclear fuel its extraordinary energy density compared to chemical fuels like coal or natural gas.
Frequently Asked Questions
What is the difference between a calorie and a kilocalorie?
A calorie (small c) is the energy needed to raise 1 gram of water by 1 degree Celsius. A kilocalorie (kcal or Calorie with capital C) is 1,000 calories. Food labels in the US show kilocalories but label them as Calories, which causes widespread confusion about energy intake.
How many joules are in a kilowatt-hour?
One kilowatt-hour equals 3,600,000 joules or 3.6 megajoules. A kWh is the energy consumed by a 1,000-watt appliance running for one hour. Electric companies charge per kWh, making it the standard unit for billing household and commercial electricity.
What is a BTU?
A British Thermal Unit is the energy needed to raise one pound of water by one degree Fahrenheit. One BTU equals about 1,055 joules. BTUs are used in the US for rating heating systems, air conditioners, and gas appliance outputs. A typical furnace might produce 80,000 BTU per hour.
What is an electronvolt?
An electronvolt is the energy gained by an electron accelerated through a 1-volt electric potential. It equals about 1.602 x 10^-19 joules. Particle physicists use electronvolts because atomic-scale energies are inconveniently small when expressed in joules.
How do I convert food calories to exercise energy?
Food calories are kilocalories. Running burns roughly 100 kcal per mile. A 300-kcal snack requires about 3 miles of running to burn off. The exact number varies by body weight, speed, and efficiency, but this rough ratio helps put food energy in perspective.