Convert Joules to Watt-Hours

Convert Joules (J) to Watt-Hours (Wh) instantly and accurately.

Conversion Formula

Wh = J × 0.0002777777778

About Joules

The joule (J) is the SI unit of energy, defined as one newton acting through one metre (1 J = 1 N·m = 1 kg·m²/s²). Named after James Prescott Joule, whose 1840s paddle-wheel experiments established the mechanical equivalent of heat (~4.15 J = 1 calorie). One joule is modest: it lifts a 100 g apple by 1 m, heats 0.239 mL of water by 1°C, or powers a 1 W LED for 1 second. Daily adult resting metabolism is ~6-9 MJ. 1 J = 1 W·s = 0.23901 cal = 9.4782 × 10⁻⁴ BTU = 2.7778 × 10⁻⁷ kWh.

About Watt-Hours

A watt-hour (Wh) is the energy delivered by 1 watt for one hour - exactly 3,600 J. It is the practical unit for small-scale electrical energy: a 10,000 mAh 5 V power bank stores 50 Wh; a laptop battery holds 50-90 Wh; a smartphone battery holds 10-15 Wh; an AA alkaline cell stores ~3 Wh. LED lamps labelled 9 W save 51 Wh/h over a 60 W incandescent. IATA dangerous-goods rules use Wh as the threshold for lithium batteries in aircraft: cells >20 Wh and batteries >100 Wh need special approval. 1 Wh = 3,600 J = 3.412 BTU.

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