What is joule?

The joule is the SI base unit of energy. It is the standard unit for work, heat, and electrical energy in physics, engineering, and scientific measurement worldwide.

Real-world uses

The joule is the SI unit of energy used in physics, chemistry, and nutrition (food energy in some countries is labelled in kilojoules). Electrical energy, mechanical work, and heat transfer are all measured in joules. One joule is the energy to lift a small apple about 1 metre.

History

Named after James Prescott Joule, the English physicist who demonstrated the mechanical equivalent of heat in the 1840s, establishing that heat and mechanical work are interchangeable forms of energy. The joule was adopted as the SI energy unit in 1960.

Common mistakes

Confusing joules with watts—a joule is a unit of energy, while a watt is a unit of power (1 W = 1 J/s). Also, assuming "calorie" and "joule" are equivalent without conversion: 1 cal = 4.184 J.

What is calorie (thermochemical)?

The thermochemical calorie is a unit of energy equal to approximately 4.184 joules. It is used in chemistry and physics to express small heat quantities, particularly in thermochemical experiments.

Real-world uses

The thermochemical calorie (4.184 J) is used in chemistry for expressing heats of reaction, specific heat capacities of substances, and calorimetry experiments. It appears in older scientific literature and some chemistry textbooks, particularly in calorimetric calculations.

History

The calorie was first defined by Nicolas Clément in 1824 as the heat needed to raise 1 gram of water by 1°C. The thermochemical calorie (exactly 4.184 J) was later standardized for precise scientific use, distinguishing it from other calorie definitions.

Common mistakes

Confusing the small calorie (cal, 4.184 J) with the large Calorie/kilocalorie (Cal/kcal, 4,184 J) used in food labelling. Also, several slightly different definitions of the calorie exist (thermochemical, 15°C, IT), which differ by fractions of a percent.

When is this conversion used?

Electricity bills use kilowatt-hours while physics calculations use joules. Converting between them is essential for energy audits, comparing appliance efficiency, and understanding power consumption.

Worked examples

1 joule = 0.23900574 calorie (thermochemical)

1 calorie (thermochemical) = 4.184 joule

How to convert joule to calorie (thermochemical)

To convert joule to calorie (thermochemical), multiply the value by 0.23900574.

To convert calorie (thermochemical) back to joule, multiply by 4.184.

Measurement standards

The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.

Did you know?

A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.

Quick reference: joule to calorie (thermochemical)

Common values

Available Energy units

• joule conversions
• kilojoule conversions
• kilowatt hour conversions
• calorie (thermochemical) conversions
• kilocalorie (dietary) conversions
• watt hour conversions
• megajoule conversions
• electronvolt conversions
• British thermal unit conversions
• therm (US) conversions

More joule conversions

• Convert joule to kilojoule
• Convert joule to kilowatt hour
• Convert joule to calorie (thermochemical)
• Convert joule to kilocalorie (dietary)
• Convert joule to watt hour
• Convert joule to megajoule
• Convert joule to electronvolt
• Convert joule to British thermal unit
• Convert joule to therm (US)

Assumption: calorie means thermochemical calorie, and therm means US therm.