What is a Celsius?

Celsius is the global temperature scale used for weather forecasts, science, medicine, and daily life in all countries except the United States. Originally proposed by Swedish astronomer Anders Celsius in 1742 (with 0° as boiling and 100° as freezing — the inverse of today's scale), the modern version was reversed shortly after his death. Since 2019, Celsius has been redefined via the Kelvin scale: 0°C is exactly 273.15 K, and 1°C equals 1 K in size. Water freezes at 0°C, boils at 100°C at sea level, and human body temperature is around 37°C. Comfortable room temperature is about 20–22°C, and a hot summer day is 30–35°C. Celsius relates to Fahrenheit by the formula °F = °C × 9/5 + 32, and to Kelvin by adding 273.15. The scale's decimal-friendly division of water's phase transitions made it the natural metric choice.

Visual reference for how the celsius relates to other temperature units. Each row links to the full converter for that pair.

• Daily weather forecasts worldwide (except US)
• Cooking temperatures in Europe, Asia, Latin America
• Body temperature on medical thermometers

• ✓0 °C = freezing; 100 °C = boiling. Easy anchor points.
• ✓Mental F conversion: double the °C and add 30 (rough). 20 °C → 70 °F (actual 68).
• ✓Medical thermometers show 0.1 °C resolution — a rise from 37.0 to 37.5 matters.

• ✗Using "degrees centigrade" — the scale was renamed Celsius in 1948.
• ✗Assuming a linear relationship between °C and °F without the +32 offset.
• ✗Interpreting UK winter forecasts in °F by habit — UK uses °C.