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Energy Converter
Convert between Joules, Calories, kWh, and BTU instantly. Understand electricity bills, food energy, and HVAC ratings.
Understanding Energy Units
Energy comes in many forms, and humans invented different units to measure it. Here's why each exists and when to use them.
Common Energy Units
- Joule (J): SI unit. 1 J = energy to lift 0.1kg by 1 meter.
- Calorie (cal): Energy to heat 1g of water by 1°C. Food uses Calories (1,000 cal).
- Kilowatt-hour (kWh): Electricity billing unit. 1 kWh = 3.6 million Joules.
- BTU: HVAC/energy industry. 1 BTU = energy to heat 1lb of water by 1°F.
⚠️ Food Label Confusion
When a food says "100 Calories", it actually means 100 kilocalories (kcal) = 100,000 calories (small cal). Scientists use lowercase 'calorie'. Food labels use uppercase 'Calorie' (1 Calorie = 1 kcal). This is why burning food in a lab releases WAY more energy than you'd expect.
Real-World Conversions
Your Electric Bill: Average US home uses ~900 kWh/month. That's 3.24 billion Joules or 774 million calories of energy.
A Banana: ~100 Calories (food) = 100,000 cal = 418,400 J = 0.116 kWh. You could theoretically power a 60W lightbulb for ~2 hours with one banana's energy.
Air Conditioner: 12,000 BTU/hr = 3.5 kW. Running 8 hours = 28 kWh = ~$3.36 (at $0.12/kWh).
Gasoline: 1 gallon = ~120,000 BTU = 126.6 million J = 35.2 kWh. Comparing gas vs electric cars? 1 gallon ≈ 35 kWh of electricity.
💡 Electricity Bill Hack
Your bill shows kWh. To find cost per hour: Divide device wattage by 1000, multiply by hours, then by your rate. Example: 1500W heater × 8 hours = 12 kWh × $0.12 = $1.44/day. Running it 24/7 for a month = ~$130!
Why So Many Units?
Humans invented units for specific contexts:
- Joules: Physics/science standard (SI unit).
- Calories: Chemistry/biology (food energy, metabolism).
- kWh: Electricity industry (easy billing).
- BTU: HVAC/energy industry (American standard).
Reviewed by Dr. Alex M.
Ph.D. in Physics
Expert in thermodynamics and energy systems.
Frequently Asked Questions
What is the difference between calories and Calories?
Lowercase 'calorie' (cal) is the small calorie used in chemistry. Uppercase 'Calorie' (Cal) is the large calorie = 1,000 cal = 1 kcal, used on food labels. When a food says '100 Calories', it means 100,000 calories (small). This converter uses small calories (cal).
How do you convert kWh to Joules?
1 kilowatt-hour (kWh) = 3,600,000 Joules. This is because 1 kW = 1,000 Watts, 1 hour = 3,600 seconds, and 1 Watt = 1 Joule/second. So: 1,000 W × 3,600 s = 3,600,000 J. Your electric bill measures energy in kWh.
What is a BTU and why is it used?
BTU (British Thermal Unit) is the energy needed to heat 1 pound of water by 1°F. It's used in HVAC (air conditioners, heaters) and energy ratings. 1 BTU = 1,055.06 Joules. Americans use BTU; the rest of the world uses Joules or kWh.