Watts to Calories Per Second (W to cal/s)

1 watt equals 0.2390057361 calories per second (rounded).

How to convert watts to calories per second

To convert watts to calories per second, multiply the number of watts by 0.2390057361. The factor is rounded to 10 significant digits. To go the other way, multiply calories per second by 4.184.

calories per second = watts × 0.2390057361

Example: 10 watts = 2.390057361 calories per second.

Several different horsepower units exist. This site lists mechanical (745.7 W), metric (735.5 W) and electrical (746 W) horsepower separately.

About these units

Watt (W)

Metric (SI)Current unit

The SI unit of power: one joule per second. A typical LED bulb uses 5–10 W and a laptop 30–60 W.

Credit for the name goes to C. William Siemens, who proposed it in August 1882 in his presidential address to the British Association for the Advancement of Science. He chose it to honor James Watt, the Scottish inventor who in 1776 improved the Newcomen steam engine. An International Conference on Electric Units and Standards adopted Siemens' definition in London in October 1908 as the international watt. After the 1948 General Conference on Weights and Measures the unit was redefined in absolute terms, and in 1960 the 11th General Conference adopted it into the SI as the unit of power.

Today one watt is one joule per second, or equivalently one volt times one ampere. Orders-of-magnitude tables put an LED light bulb at about 7 W and an adult's basal metabolic rate at roughly 100 W. A 100 kg person climbing a 3 m ladder in 5 seconds works at about 600 W, while a laborer can sustain around 75 W over an eight-hour day. The watt measures a rate, so it says how fast energy is being used, not how much has been used in total.

The watt is the reference unit for power on this site.

Sources: Wikipedia: Watt; Wikipedia: Orders of magnitude (power)

Calorie Per Second (cal/s)

ScientificTraditional unit (still used in some regions)

Exactly 4.184 watts.

Pairing the small calorie with the second yields a unit that fits laboratory work, where heat flows are modest and timed in seconds. With the thermochemical calorie, defined as exactly 4.184 joules, one calorie per second is exactly 4.184 watts. NIST lists the thermochemical calorie per second at 4.184 watts as an exact factor, and the same list gives the kilocalorie per second as 4,184 watts.

The 15 degree calorie is a little different at about 4.1855 joules, and the International Table calorie of 1956 is 4.1868 joules, so a rate quoted in calories per second without a qualifier can differ by a few parts in ten thousand. The calorie itself is regarded as obsolete since the joule became the official SI unit of energy in 1948, and the watt, one joule per second, has replaced this rate in current work.

1 calorie per second = 4.184 watts (exactly).

Sources: NIST SP 811, Appendix B.8; Wikipedia: Calorie

Related conversions

See all power units.