Convert Millijoules to Watt-Hours
Convert Millijoules (mJ) to Watt-Hours (Wh) instantly and accurately.
Conversion Formula
Wh = mJ × 2.777777778e-7
About Millijoules
A millijoule (mJ) is 10⁻³ J - the scale of surgical lasers, spark ignition, and the kinetic energy of small everyday objects. Nd:YAG lasers for ophthalmology and tattoo removal deliver 10-200 mJ per pulse. The minimum spark energy to ignite methane-air is ~0.29 mJ; an automotive spark plug discharges 30-60 mJ per cycle. A 2 g mosquito flying at 1 m/s has kinetic energy ½ × 0.002 × 1² = 1 mJ. Electrocautery monopolar pulses deliver 50-500 mJ to coagulate blood vessels. 1 mJ = 10⁻³ J = 0.2390 cal.
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.
Quick Reference Table
| Millijoules (mJ) | Watt-Hours (Wh) |
|---|---|
| 1 mJ | 2.778 × 10-7 Wh |
| 2 mJ | 5.556 × 10-7 Wh |
| 5 mJ | 1.389 × 10-6 Wh |
| 10 mJ | 2.778 × 10-6 Wh |
| 25 mJ | 6.944 × 10-6 Wh |
| 50 mJ | 1.389 × 10-5 Wh |
| 100 mJ | 2.778 × 10-5 Wh |