Energy Converter: How to Convert Between Joules, Calories, kWh, and BTUs

Energy units appear everywhere — your electricity bill uses kilowatt-hours (kWh), food labels show Calories, physics problems use joules (J), and heating systems are rated in BTUs. Converting between these units is essential for comparing energy costs, tracking fitness goals, or understanding appliance efficiency. Our Energy Converter handles all common units instantly, but knowing the key relationships helps you make sense of the numbers.

Energy Units Reference Table

Unit	Symbol	Common Use	Equivalent
Joule	J	SI unit, physics, science	Base unit
Kilojoule	kJ	Food energy (Australia/NZ), exercise	1,000 J
Calorie	cal	Food energy (US), chemistry	4.184 J
Kilocalorie	kcal	Food labels (“Calories” with capital C)	4,184 J
Kilowatt-hour	kWh	Electricity billing, appliances	3,600,000 J (3.6 MJ)
BTU	BTU	HVAC, heating, cooling systems	1,055 J
Therm	therm	Natural gas billing	105,500,000 J (100,000 BTU)
Electronvolt	eV	Particle physics, quantum mechanics	1.602 × 10⁻¹⁹ J

Real-World Energy Examples

• Your morning coffee: A 200-calorie latte = 837 kJ = 0.23 kWh of energy
• Running for 30 minutes: Burns about 300 Calories (1,255 kJ) — enough to power a 60W light bulb for 5.8 hours
• One kWh of electricity: Powers a refrigerator for about 24 hours, or runs a laptop for approximately 50 hours
• Natural gas bill: A typical home uses 50–150 therms per month in winter. 1 therm = 100,000 BTU = 29.3 kWh
• Gasoline: One gallon contains about 33.7 kWh of energy. Only about 20–30% reaches the wheels (engine efficiency)

Use our Energy Converter to compare energy values across different units — perfect for understanding utility bills, nutrition, or engineering projects.

Common Conversion Mistakes

• Calorie vs Calorie: Food labels use kcal (1,000 cal). When a label says “200 Calories,” it means 200 kcal = 200,000 cal. Always divide by 1,000 when converting food energy to physics calories
• kWh vs kW: Power (kW) is the rate, energy (kWh) is the total. A 2 kW heater running for 3 hours uses 6 kWh of energy. Don’t confuse rate with total
• BTU per hour vs BTU: HVAC ratings in “BTU” usually mean BTU per hour. A 12,000 BTU air conditioner consumes about 12,000 BTU of energy per hour of operation

Get instant, accurate energy conversions with the Energy Converter — supports joules, calories, kWh, BTUs, therms, and more.