The watt (W) is the SI base unit of power, defined as one joule per second, measuring the rate of energy transfer. From light bulb brightness ratings to phone charger output, the watt appears in everyday product specifications worldwide. One watt equals exactly 1 joule per second, or about 0.001341 horsepower.

Calories per second (cal/s) equals exactly 4.184 watts, used primarily in thermodynamics and physics to express heat transfer rates. While not a common everyday unit, it bridges thermal and mechanical power calculations in scientific research. One calorie per second equals exactly 4.184 watts or about 0.00561 horsepower.