Energy and Work Unit Converter

Convert between energy and work units including joules, kilowatt-hours, calories, BTU, electronvolts, and more.

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Understanding Energy and Work

What is a Joule?

The joule (J) is the SI unit of energy and work. One joule is defined as the amount of energy transferred when one newton of force moves an object one meter.

Energy = Power × Time

Energy and power are related by time. If you know the power consumption (watts) and duration (seconds or hours), you can calculate energy.

Example: A 100-watt light bulb running for 10 hours uses 100 W × 10 h = 1,000 Wh = 1 kWh of energy.

Kilowatt-hours (kWh)

The kilowatt-hour is the standard unit for electricity billing. One kWh equals 3.6 megajoules (3,600,000 J). A typical US household uses about 30 kWh per day, or 900 kWh per month.

Calorie vs calorie: A Critical Distinction

The word "calorie" has two different meanings depending on capitalization, which creates confusion in nutrition and science:

British Thermal Unit (BTU)

The BTU is commonly used in HVAC and heating systems in the United States. One BTU is approximately 1,055 joules. Air conditioner capacity is rated in BTU/hr (e.g., 12,000 BTU/hr = 1 ton of cooling).

TNT Equivalent

The ton of TNT is a unit used to describe the energy released in explosions. It's defined as exactly 4.184 gigajoules (1 billion calories). Nuclear weapons are measured in kilotons (thousands of tons) or megatons (millions of tons) of TNT equivalent.

Electronvolt (eV)

The electronvolt is the standard energy unit in atomic and particle physics. One eV is the kinetic energy gained by an electron accelerated through a potential difference of one volt.

X-rays: keV range • Gamma rays: MeV range • Particle accelerators: GeV-TeV range

Energy Conservation

The First Law of Thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. When you lift an object, chemical energy from your muscles converts to gravitational potential energy. When it falls, that converts to kinetic energy, then to heat and sound upon impact.

Energy Density Comparison

Common Fuel Energy Content

• Gasoline: ≈ 46 MJ/kg or ≈ 120 MJ/gallon
• Diesel: ≈ 45 MJ/kg or ≈ 130 MJ/gallon (denser than gasoline)
• Natural gas: ≈ 55 MJ/kg or ≈ 37 MJ/m³
• Coal (bituminous): ≈ 24-35 MJ/kg
• Wood (dry): ≈ 16 MJ/kg

Human Energy Expenditure

• Basal metabolic rate: ≈ 1,400-1,800 Cal/day (5.9-7.5 MJ/day)
• Walking (moderate pace): ≈ 280 Cal/hour (1.17 MJ/hour)
• Running (6 mph): ≈ 600 Cal/hour (2.51 MJ/hour)
• Cycling (moderate): ≈ 400 Cal/hour (1.67 MJ/hour)

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Most Common Conversions

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Quick Reference Cards

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Energy Examples

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