Energy Converter

About the Energy Converter

An energy converter transforms between joules (J), kilojoules (kJ), calories (cal, the small calorie), kilocalories (kcal, also written as Calories with a capital C on food labels), watt-hours (Wh), kilowatt-hours (kWh), British thermal units (BTU), electronvolts (eV), and therms. Energy conversion is needed in nutrition (understanding food Calories), electricity billing (kWh), heating and cooling (BTU), physics and chemistry (joules and eV), and engineering. The most widespread confusion: food labels list "Calories" which are actually kilocalories (kcal) — one food Calorie = 1,000 physics calories. Our converter makes this explicit and handles all common energy unit systems with 12-digit precision.

How It Works

Base unit: joule (J). Key conversions: 1 cal (thermochemical) = 4.184 J. 1 kcal (food Calorie) = 4,184 J = 4.184 kJ. 1 Wh = 3,600 J. 1 kWh = 3,600,000 J = 3.6 MJ = 3,412.14 BTU. 1 BTU = 1,055.06 J = 0.293 Wh = 252.164 cal. 1 eV = 1.602 × 10⁻¹⁹ J (used for atomic-scale energies). 1 therm = 100,000 BTU = 29.307 kWh (used for natural gas billing). Example: a 500 Calorie meal = 500 kcal = 2,092 kJ = 0.581 kWh. Running 1 mile burns approximately 100 kcal = 418,400 J = 0.116 kWh — enough to power a 100W light bulb for about 1.16 hours.

Tips & Best Practices

• ✓Food label confusion: "200 Calories" on a food label means 200 kilocalories (kcal) = 200,000 small calories. The capital C is the technical convention, but it is widely misunderstood.
• ✓Electricity cost: 1 kWh is the energy used by a 1,000W appliance for 1 hour. At $0.15/kWh, running a 1,500W space heater for 8 hours costs 1,500×8/1,000 × $0.15 = $1.80.
• ✓BTU for HVAC: air conditioners are rated in BTU per hour (BTU/h). A 12,000 BTU/h unit = 3,517 watts = 3.517 kW cooling capacity = "1 ton" of cooling.
• ✓Natural gas billing: gas is billed in therms (100,000 BTU each) or CCF (hundred cubic feet). 1 therm = approximately 29.3 kWh of heat energy.
• ✓Gasoline energy: 1 US gallon of gasoline contains approximately 132 MJ = 36.6 kWh of chemical energy. A car at 30 MPG uses 36.6 kWh per 30 miles = 1.22 kWh per mile.
• ✓Human metabolism: a sedentary adult burns approximately 2,000 kcal per day = 8,368 kJ = 2.32 kWh. This is the average daily energy requirement used on nutrition labels.
• ✓eV in particle physics: chemical bond energies are a few eV. Nuclear reactions release millions of eV (MeV). The LHC collides protons at 13 TeV (13 × 10¹² eV).
• ✓1 joule is small: lifting an apple (100g) by 1 metre requires approximately 1 joule of work. A 100W light bulb uses 100 joules every second.

Who Uses This Calculator

Nutritionists and dietitians converting food energy measurements. Electricians and energy auditors calculating appliance energy use and costs. HVAC engineers sizing heating and cooling systems using BTU ratings. Physicists and chemists working across energy unit systems. Students completing physics and chemistry energy calculations. Homeowners understanding gas and electricity billing unit differences. Environmental analysts comparing energy content of different fuels.