Temperature is a measure of hot or cold, typically taken with a thermometer. Common scales include Celsius (°C), Fahrenheit (°F), and Kelvin (K). Absolute zero, the coldest possible temperature, is 0 K, −273.15 °C, or −459.67 °F, where atomic motion almost stops. In the SI system, the kelvin is the base unit, but Celsius is commonly used for daily purposes, with 0°C marking ice's melting point and 100°C as water’s boiling point at sea level. The Celsius and Kelvin scales are offset by 273.15, meaning a 1°C change equals 1 K. By agreement, the Kelvin and Celsius scales are based on absolute zero and the triple point of water (273.16 K, 0.01 °C). In the U.S., Fahrenheit is used, with 32 °F as water’s freezing point and 212 °F as its boiling point.
