Among a number of temperature scales developed over time, three have been favored (more than the others): Celsius, Kelvin and Fahrenheit. In the metric system, Celsius scale is preferred. Almost all the countries (with a major exception of US) use the metric scale.
Scientists use the Celsius scale for two main reason: In the Celsius scale the freezing and boiling points of water are 100 units (or degrees Celsius) apart, freezing point being 0 degrees Celsius and boiling point being set at 100 degrees Celsius. In comparison, the Fahrenheit scale has the same difference set at 180 units. Hence, the Celsius scale is just easier to use. In addition, Celsius and Kelvin (another commonly used scale, especially by scientists) have the same unit size, with the difference between scales set at 273 units. In simpler terms, absolute temperature where life seizes to exist is given as -273 degrees Celsius or 0 K.