Is Wh the same as Joules?

No. 1 Wh = 3.6 kJ = 3,600 J. They measure the same thing (energy), but Wh encodes a time scale (power × hour), while joules are instantaneous. The conversion factor 3.6 comes from 1 watt × 3,600 seconds (1 hour).

Why use Wh if we have kilojoules?

Watt-hours are intuitive for batteries. A 20 Wh phone battery running at 4W lasts 5 hours — easy math. Kilojoules (72 kJ) require division: 72 ÷ 14,400 (4W × 3,600s) = 5 hours. Wh directly encodes 'hours of runtime' at 1-watt power; that's why it's consumer-standard.

How many Wh are in a AA battery?

A typical AA alkaline battery: 1.5 volts × 3,000 mAh = 4.5 Wh (16.2 kJ). Rechargeable AA (NiMH): 1.2 volts × 2,500 mAh = 3 Wh (10.8 kJ). Lower voltage than alkaline, but sufficient for most devices.

What's the relationship between Wh and mAh?

Wh = (mAh × voltage) ÷ 1000. For a 3.7V lithium battery with 3000 mAh: (3000 × 3.7) ÷ 1000 = 11.1 Wh = 40 kJ. The voltage rating is critical; always check it when comparing batteries by mAh alone.

Watt-Hours (Wh) to Kilojoules (kJ) Converter

Enter a value to instantly convert between energy units.

From

Precision4 dp

1 Watt-Hour = 3.6 Kilojoule

Key Formulas

Kilocalorie → Kilojoule

kJ = kcal × 4.184

Kilojoule → Kilocalorie

kcal = kJ × 0.239006

Kilowatt-Hour → Joule

J = kWh × 3600000

Joule → Kilowatt-Hour

kWh = J × 2.77778e-7

Formula

kJ = Wh × 3.6

Watt-hours are the practical standard for portable electronics (batteries, power banks, tools), while kilojoules are the SI unit for all energy. You convert Wh to kJ when comparing device energy storage across specification sheets and technical standards, when calculating total energy in complex systems that mix electrical (Wh) and thermal (kJ) components, or when translating consumer device specs into engineering or scientific documentation.

Source: NIST SP 811, Table B.8

Frequently Asked Questions

Real-World Examples

A smartphone engineer converting battery capacity. 15 Wh (a typical phone battery) = 54 kJ. Over 500 charge cycles: 15 Wh × 500 = 7,500 Wh = 27,000 kJ, the total energy the battery delivers during its lifespan.

15 Wh = 54 kJ

A portable power bank spec. A 100 Wh capacity (360 kJ) can charge a 15 Wh phone (~6 times) or power a 10W LED lamp for 10 hours. In SI terms, it's a modest 360 kJ, highlighting why kilojoules seem huge for daily devices.

100 Wh = 360 kJ

A wireless earbud case spec. 5 Wh charging capacity (18 kJ) provides multiple earbud charges. For comparison, a smartphone battery is ~3× larger in energy, yet feels like 'small amounts' for both everyday electronics.

5 Wh = 18 kJ

An emergency backup battery for medical equipment. 500 Wh UPS (1,800 kJ) runs a 100W device for 5 hours, or a 50W monitor all day. In SI units: 1.8 megajoules, the scale of serious backup systems.

500 Wh = 1800 kJ

kcal to kj kj to kcal kwh to joules joules to kwh btu to joules calories to joules

Watt-Hours (Wh) to Kilojoules (kJ) Converter

Key Formulas

Formula

Frequently Asked Questions

Real-World Examples

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