⚡ Energy and Power Conversion Guide
Complete energy conversion guide — food calories, kilowatt-hours, BTU, joules, plus power: watts, kilowatts, mechanical hp, metric PS.
Energy and power are related but distinct. Energy is a quantity — kWh in your battery, kcal you burn, BTU from your furnace. Power is the rate — how fast energy flows through wires.
The SI chain
One joule = energy to accelerate 1 kg by 1 m/s^2. One watt = 1 joule/sec. One kWh = 1,000 W x 3,600 sec = 3.6 million joules. Your electricity bill charges by the kWh.
Food calories
Nutrition labels say Calories but mean kilocalories. 1 food Calorie = 1 kcal = 4,184 J. An adult burns 2,000-2,500 kcal/day. Running 5 km = 300-400 kcal.
Fuel economy
UK gallon (4.546 L) is 20% larger than US gallon (3.785 L). 50 UK MPG = 41.7 US MPG. European L/100km is inverse — lower is better. 5.0 L/100km = 47.0 US MPG.
Related converters
Frequently asked questions
Difference between energy and power?
Energy is a quantity (kWh, kcal, BTU). Power is energy PER TIME (watts = J/sec, hp = 550 ft-lb/sec). A 60W bulb using 1 kWh runs 16.7 hours.
How many calories in a kWh?
1 kWh = 3.6M J = 860.4 kcal. Your fridge uses about 1 kWh per day.
Why two horsepower values?
Mechanical hp (US) = 745.7 W. Metric PS = 735.5 W. 1.4% difference.
Is a Calorie the same as a calorie?
No. Food Calorie (capital C) = 1 kcal = 4,184 J.
Last updated — conversions use exact ISO unit definitions.