Temperature

Temperature measures the average kinetic energy of particles in a substance — the faster particles move, the higher the temperature. Three scales are in common use worldwide: Celsius (the international standard for everyday use), Fahrenheit (used in the United States), and Kelvin (the SI base unit used in science). Unlike length or mass, temperature scales do not simply scale by a multiplication factor; converting between them requires both multiplication and an additive offset because the scales have different zero points.

Units

Degrees Celsius (°C): The SI-aligned scale where 0°C is the freezing point of water and 100°C is the boiling point at standard sea-level pressure. Named after Anders Celsius (1742). Scale: Human body temperature is approximately 37°C; room temperature is typically 20–22°C. Example: Water freezes at 0°C and boils at 100°C.
Degrees Fahrenheit (°F): The scale used in the United States, where 32°F is the freezing point of water and 212°F is the boiling point. Named after Daniel Gabriel Fahrenheit (1724). Scale: Normal body temperature is 98.6°F; comfortable room temperature is approximately 68–72°F. Example: Most home ovens are set between 300°F and 450°F for baking.
Kelvin (K): The SI base unit of thermodynamic temperature, defined since 2019 by fixing the Boltzmann constant to exactly 1.380 649 × 10⁻²³ J/K. 0 K is absolute zero — the coldest possible temperature. Scale: Water freezes at 273.15 K and boils at 373.15 K. Room temperature is approximately 295 K. Example: The surface of the Sun is approximately 5 778 K.

Key Facts

−40°C equals −40°F — the only point where Celsius and Fahrenheit intersect.
Absolute zero (0 K = −273.15°C) is the theoretical minimum temperature; no object has ever been cooled to exactly 0 K.
The Kelvin scale uses the same degree size as Celsius — only the zero point differs.
Anders Celsius originally proposed 0° as boiling and 100° as freezing; the scale was inverted after his death.
The Boltzmann constant (k = 1.380 649 × 10⁻²³ J/K) now defines the kelvin — linking temperature to energy at the quantum level.

Open the Temperature converter