What is watt hour?

A watt hour is a unit of energy equal to the power of one watt sustained for one hour. It is used to measure small amounts of electrical energy consumption, particularly in battery capacities and portable electronics.

Real-world uses

Watt-hours measure the energy stored in or consumed from batteries, small electronics, and portable power stations. A smartphone battery holds roughly 10–15 Wh; a laptop battery 40–100 Wh. Solar panel output for small installations is often quoted in Wh per day.

History

The watt-hour emerged as a practical energy unit in the late 19th century with the commercialisation of electric power distribution. It offered a convenient scale between the joule (too small) and kilowatt-hour (too large) for everyday portable energy applications.

Common mistakes

Confusing watt-hours (energy) with watts (power). A device rated at 5 W running for 3 hours consumes 15 Wh. Also, treating Wh and mAh as interchangeable without knowing voltage: Wh = mAh × V ÷ 1000.

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?

Converting watt hour to calorie (thermochemical) is useful in the energy domain when comparing values across different measurement standards or applying formulas that require a specific unit.

Worked examples

1 watt hour = 860.4206501 calorie (thermochemical)

1 calorie (thermochemical) = 4.184 joule

How to convert watt hour to calorie (thermochemical)

To convert watt hour to calorie (thermochemical), multiply the value by 860.4206501.

To convert calorie (thermochemical) back to watt hour, multiply by 0.00116222.

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: watt hour 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 watt hour conversions

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

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