Kiloelectronvolts to Watt-hours (keV to Wh)

1 kiloelectronvolt equals 4.45049065×10⁻²⁰ watt-hours exactly.

1 kiloelectronvolt = 4.45049065×10⁻²⁰ watt-hours

How to convert kiloelectronvolts to watt-hours

To convert kiloelectronvolts to watt-hours, multiply the number of kiloelectronvolts by 4.45049065×10⁻²⁰. This factor is exact. To go the other way, multiply watt-hours by 2.246943267×10¹⁹ (rounded).

watt-hours = kiloelectronvolts × 4.45049065×10⁻²⁰

Example: 10 kiloelectronvolts = 4.45049065×10⁻¹⁹ watt-hours.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Kiloelectronvolt (keV)

ScientificCurrent unit

1,000 electronvolts. X-ray photon energies are in this range.

X-rays are the usual home of the keV. Wilhelm Roentgen discovered them on 8 November 1895, and their photon energies span about 100 eV to 100 keV. Photons above roughly 5 to 10 keV count as hard X-rays, while lower ones are soft. Medical diagnostic tubes run at 20 to 150 kilovolts, which sets the highest photon energies of a radiograph at about 20 to 150 keV. One keV is 1.602176634 x 10^-16 J.

Fusion research uses it for temperature. A magnetic confinement plasma at about 15 keV corresponds to roughly 174 million kelvin. Compared with the electronvolt, a kiloelectronvolt is a thousand times larger, so it lies well above the 1 to 10 eV of chemical bonds, yet far below the millions of electronvolts released in nuclear reactions.

1 kiloelectronvolt = 1.602176634×10⁻¹⁶ joules (exactly).

Sources: Wikipedia: X-ray; Wikipedia: Electronvolt

Watt-hour (Wh)

Metric (SI)Current unit

Exactly 3,600 joules, the energy used by a one-watt device in an hour. Battery capacities are quoted in watt-hours.

Pair a power unit with a unit of time and you get the watt-hour: one watt sustained for one hour, which works out to 3,600 joules. The watt itself was adopted at the second International Electrical Congress in 1889, in the same session that adopted the joule, so the two units share a birthday even though the watt-hour is the one people read off batteries.

Battery capacity is where it earns its keep. Multiplying amp-hours by the battery voltage gives an estimate of watt-hours, so a 2,500 mAh lithium-ion cell at 3.7 V holds roughly 9.25 Wh. That is why a 500 mA USB device runs about 3.7 hours on it rather than five: the cell voltage, not the 5 V from the port, sets the energy.

For scale, an alkaline AA battery holds about 9 kJ, which is 2.5 Wh. A 12 W LED lamp left on for an hour uses 12 Wh, and a 40 W appliance running for 25 hours uses 1,000 Wh.

1 watt-hour = 3,600 joules (exactly).

Sources: Wikipedia: Watt-hour; Wikipedia: Joule; Wikipedia: Orders of magnitude (energy)

Related conversions

See all energy units.