Energy Converter

The distinction between "Calories" (with a capital C) and "calories" (with a lowercase c) is important in nutrition and energy measurements:

• calorie (cal): A small calorie or gram calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1°C. This is the scientific definition and equals 4.184 joules.
• Calorie (Cal): A large calorie, food calorie, or kilocalorie (kcal) is the amount of energy needed to raise the temperature of 1 kilogram of water by 1°C. This equals 1,000 small calories or 4,184 joules.

In nutrition and food labeling, "Calories" (with a capital C) are used, which are actually kilocalories. For example:

• When a food label states "200 Calories," it means 200 kilocalories (kcal) or 200,000 small calories
• This equals about 837 kilojoules (kJ) of energy
• A chocolate chip cookie might contain 150 Calories (kcal), which is 150,000 calories (cal)

This distinction can be confusing, which is why many countries now use kilojoules (kJ) on food labels instead of kilocalories or Calories.

Converting between electrical energy units (like kilowatt-hours) and other energy units is straightforward because energy is measured the same way regardless of form:

Practical examples:

• If your electricity bill shows you used 1,000 kWh last month, that's equivalent to 3,600 MJ of energy
• A 100-watt light bulb operating for 10 hours consumes 1 kWh of electrical energy
• To convert your home's electrical consumption to the equivalent in natural gas (often measured in therms), multiply kWh by 0.03412 to get therms

Note that when converting between different forms of energy (not just units), efficiency factors come into play. For example, converting natural gas to electricity in a power plant is typically only 30-45% efficient.

Different industries and fields have standardized on particular energy units:

When working across industries, energy converters are essential for translating between different customary units. The trend in scientific and international contexts is moving toward standardized SI units (joules), but industry-specific units remain widespread in practice.

Here's a comparison of energy content in various foods and fuels:

Foods (per 100g):

Fuels (per kg or L):

Interesting Energy Comparisons:

• A single AA battery contains about 3.9 Wh (14 kJ) of energy
• A typical smartphone battery holds about 10-12 Wh (36-43 kJ)
• A chocolate bar (~50g) contains around 250 kcal (1,050 kJ), which could power a 100W light bulb for ~3 hours if converted perfectly
• A gallon of gasoline contains about 33.7 kWh of energy, equivalent to the electricity used by an average US home over ~1.1 days

This demonstrates why fossil fuels have been so economically dominant—they pack enormous energy in a small volume compared to other sources, though with significant environmental consequences.

In physics and chemistry, energy units are used in specialized ways across different subdisciplines:

Energy conversion factors relevant to physics and chemistry:

• 1 eV = 1.602 × 10⁻¹⁹ joules
• 1 eV = 96.49 kJ/mol (for a mole of particles)
• 1 eV = 8,065.5 cm⁻¹ (wavenumbers)
• 1 eV = 2.417 × 10¹⁴ Hz (frequency)
• 1 kcal/mol = 4.184 kJ/mol

These specialized energy units are chosen to make calculations more convenient at various size scales, from the subatomic to the macroscopic.

Power and energy are closely related but distinct concepts:

The mathematical relationship:

Or in units:

Everyday examples:

• A 60-watt light bulb (power) running for 10 hours consumes 600 watt-hours (energy)
• A 2000-watt hairdryer used for 5 minutes uses 167 watt-hours of energy
• A car might have an engine rated at 150 horsepower (power) but travels on 15 gallons of gasoline (energy)
• A 3000-calorie meal contains enough energy to power a 100-watt bulb for about 35 hours

This relationship is why we pay electric bills in kilowatt-hours (energy) rather than kilowatts (power). Power tells you the instantaneous rate of consumption, while energy tells you the total amount consumed over time.