What is a Watt-Hour?

The watt-hour is the standard unit for small-battery capacity, household electricity, and renewable-energy storage.

Overview

The watt-hour equals exactly 3,600 joules and is the standard unit for small-battery capacity, household electrical energy, and renewable-energy storage. A smartphone battery stores roughly 12–15 Wh, a laptop battery 50–100 Wh, and an electric car battery 60,000–100,000 Wh (60–100 kWh). The watt-hour represents the energy delivered by a 1-watt device running for 1 hour. It is the natural unit for connecting power (watts) to time, which is why electric utilities bill in kilowatt-hours. The watt-hour relates to the joule (3,600 J = 1 Wh), the kilowatt-hour (1,000 Wh = 1 kWh), and the BTU (1 Wh ≈ 3.412 BTU). Battery capacity, solar panel output (Wh per day), and energy storage system specifications all rely on the watt-hour as the base small-energy unit.

Symbol

Convert Watt-Hour to all units

Live result

Joule3,600 J Kilojoule3.6 kJ Megajoule0.0036 MJ Kilowatt-Hour0.001 kWh Calorie860.42065 cal Kilocalorie0.860421 kcal British Thermal Unit3.412142 BTU Electronvolt2.247 × 10^22 eV Therm0.00003412 thm

Relationship to Other Energy Units

1 Wh equals

Visual reference for how the watt-hour relates to other energy units. Each row links to the full converter for that pair.

1 Wh=3,600 J 1 Wh=3.6 kJ 1 Wh=0.0036 MJ 1 Wh=0.001 kWh 1 Wh=860.42065 cal 1 Wh=0.860421 kcal 1 Wh=3.412142 BTU 1 Wh=2.247 × 10^22 eV 1 Wh=0.00003412 thm

When Is the Watt-Hour Used?

Laptop and phone battery capacity
Portable power banks and UPS
Home solar panel daily output

Real-world examples

iPhone battery: 12 Wh. MacBook Pro: 70 Wh. Power bank: 20 Wh–100 Wh. Airplane carry-on limit: usually 100 Wh.

Tips for Using the Watt-Hour

1 Wh = 3600 J = 0.001 kWh.
Battery mAh × V = Wh. A 3000 mAh phone battery at 3.7 V = 11.1 Wh.
Airline limits lithium batteries to 100 Wh for carry-on.

Common Mistakes

Confusing mAh with Wh — need voltage to convert.
Using Wh when kWh is more appropriate for large batteries.
Forgetting the voltage in battery capacity calculations.

Convert Watt-Hour to Other Energy Units

Watt-Hour to Joule

1 Wh = 3,600 J

Watt-Hour to Kilojoule

1 Wh = 3.6 kJ

Watt-Hour to Megajoule

1 Wh = 0.0036 MJ

Watt-Hour to Kilowatt-Hour

1 Wh = 0.001 kWh

Watt-Hour to Calorie

1 Wh = 860.42065 cal

Watt-Hour to Kilocalorie

1 Wh = 0.860421 kcal

Watt-Hour to British Thermal Unit

1 Wh = 3.412142 BTU

Watt-Hour to Electronvolt

1 Wh = 2.247 × 10^22 eV

Watt-Hour to Therm

1 Wh = 0.00003412 thm

Convert Other Units to Watt-Hour

Joule to Watt-Hour

1 J = 0.000278 Wh

Kilojoule to Watt-Hour

1 kJ = 0.277778 Wh

Megajoule to Watt-Hour

1 MJ = 277.77778 Wh

Kilowatt-Hour to Watt-Hour

1 kWh = 1,000 Wh

Calorie to Watt-Hour

1 cal = 0.001162 Wh

Kilocalorie to Watt-Hour

1 kcal = 1.162222 Wh

British Thermal Unit to Watt-Hour

1 BTU = 0.293071 Wh

Electronvolt to Watt-Hour

1 eV = 4.45 × 10^-23 Wh

Therm to Watt-Hour

1 thm = 29,307.107 Wh

FAQ About the Watt-Hour

3 questions

What does the Watt-Hour (Wh) measure?

The watt-hour measures energy. The watt-hour is the standard unit for small-battery capacity, household electricity, and renewable-energy storage.

When is the Watt-Hour used?

The watt-hour is used in: Laptop and phone battery capacity; Portable power banks and UPS; Home solar panel daily output. iPhone battery: 12 Wh. MacBook Pro: 70 Wh. Power bank: 20 Wh–100 Wh. Airplane carry-on limit: usually 100 Wh.

How accurate are conversions involving the Watt-Hour?

All conversions on Units Converter use NIST SP 811 and BIPM reference values, accurate to 8 significant figures.