What Is Celsius (°C)?
Celsius is a common way to measure temperature. It tells us how hot or cold something is, using a scale where water freezes at 0 degrees and boils at 100 degrees at normal air pressure.
This scale is used in most countries for weather reports, cooking, science, and everyday life. If you see a number followed by °C, that number is in degrees Celsius.
Definition
Celsius is a unit used to measure temperature. The symbol is °C, which stands for degrees Celsius.
The Celsius scale is built around the behavior of pure water at standard air pressure.
- 0 °C is the temperature where pure water turns to ice.
- 100 °C is the temperature where pure water turns to steam.
The distance between 0 °C and 100 °C is divided into 100 equal parts. Each part is one degree Celsius. This makes Celsius a metric unit, which fits with other metric units like meter and kilogram.
In science, Celsius is closely linked to the Kelvin scale. The Kelvin scale starts at absolute zero, which is the coldest possible temperature. The size of one degree is the same in Celsius and Kelvin, only the starting point is different.
History / Origin
The Celsius scale was created in the 1700s by a Swedish astronomer named Anders Celsius. He lived in the city of Uppsala and studied the stars and weather.
Anders Celsius first suggested a temperature scale where:
- 0 degrees was the boiling point of water.
- 100 degrees was the freezing point of water.
After he died, other scientists found this confusing and decided to flip the scale. They changed it so that 0 °C is freezing and 100 °C is boiling. This is the version we still use today.
For a long time, the scale was called the centigrade scale because there are 100 degrees between freezing and boiling. Later, to avoid confusion with other uses of the word centigrade, the official name became Celsius, in honor of Anders Celsius.
Symbol & Abbreviation
The symbol for Celsius is °C.
- The small circle is called the degree sign.
- The capital letter C stands for Celsius.
We write temperatures like this:
- 20 °C for twenty degrees Celsius.
- -5 °C for five degrees below zero Celsius.
Notice there is usually a small space between the number and the symbol, like 25 °C. Both in science and in everyday life, people understand °C to mean degrees Celsius.
Current Use Around the World
Celsius is the main temperature scale in most of the world.
- Most countries use Celsius for weather, cooking, school, and science.
- Scientific work often uses Celsius along with Kelvin, because they are closely related.
- Medicine uses Celsius to describe body temperature, for example 37 °C for a normal body temperature.
A few countries, like the United States, still use Fahrenheit for many daily things such as weather reports. However, even in those places, scientists, doctors, and many technical fields also use Celsius.
Because Celsius is part of the metric system, it fits well with other metric units. This is one reason it is taught in schools all over the world.
Example Conversions
It is often useful to change a temperature from Celsius to other scales or the other way around. Here are some simple rules and examples.
Between Celsius and Fahrenheit
To convert Celsius to Fahrenheit:
Fahrenheit = Celsius × 9 ÷ 5 + 32
To convert Fahrenheit to Celsius:
Celsius = (Fahrenheit – 32) × 5 ÷ 9
Examples:
- 0 °C → Fahrenheit: 0 × 9 ÷ 5 + 32 = 32 °F
- 20 °C → Fahrenheit: 20 × 9 ÷ 5 + 32 = 68 °F
- 100 °C → Fahrenheit: 100 × 9 ÷ 5 + 32 = 212 °F
- 32 °F → Celsius: (32 – 32) × 5 ÷ 9 = 0 °C
- 68 °F → Celsius: (68 – 32) × 5 ÷ 9 = 20 °C
Between Celsius and Kelvin
The Kelvin scale is used a lot in physics and chemistry. It has the same size degree as Celsius but starts at absolute zero.
- To go from Celsius to Kelvin: K = °C + 273.15
- To go from Kelvin to Celsius: °C = K – 273.15
Examples:
- 0 °C → Kelvin: 0 + 273.15 = 273.15 K
- 25 °C → Kelvin: 25 + 273.15 = 298.15 K
- 300 K → Celsius: 300 – 273.15 = 26.85 °C
Common Real World Temperatures in Celsius
- Ice melts and water freezes around 0 °C.
- A cool room might be 15 °C.
- A comfortable room is often around 20 to 22 °C.
- Normal human body temperature is about 37 °C.
- Hot bath water may be around 40 °C.
- Boiling water is about 100 °C at sea level air pressure.
Related Units
Celsius is one of several temperature units. Here are some closely related ones.
- Kelvin (K)
Used in science. One Kelvin is the same size step as one degree Celsius. The Kelvin scale starts at absolute zero, which is about -273.15 °C. - Fahrenheit (°F)
Mostly used in the United States for weather and everyday life. Water freezes at 32 °F and boils at 212 °F. - Rankine (°R or °Ra)
Used in some engineering fields. It is like Fahrenheit but starts at absolute zero, similar to how Kelvin relates to Celsius. - Degree
This word simply means a step on a temperature scale. Degree Celsius and degree Fahrenheit both use the word degree but are different sizes.
All of these units measure the same thing, temperature. They just use different starting points and step sizes.
FAQs
What is Celsius used for?
Celsius is used to measure temperature. People use it for weather, cooking, body temperature, school experiments, and many kinds of science.
What is normal body temperature in Celsius?
Normal body temperature for a healthy adult is usually around 37 °C when measured inside the mouth. Some people can be a little lower or higher and still be healthy.
Why do many countries use Celsius instead of Fahrenheit?
Many countries use Celsius because it is part of the metric system, which is simple and widely used for other measurements like length and weight. The scale is easy to understand because it is based on water freezing at 0 °C and boiling at 100 °C.
Is Celsius a metric unit?
Yes. Celsius is the temperature unit in the International System of Units, often called the metric system. It works well with other metric units used worldwide.
What is absolute zero in Celsius?
Absolute zero is the coldest possible temperature. It is about -273.15 °C. At this temperature, the tiny particles that make up matter have as little motion as possible.
How is Celsius related to Kelvin?
Celsius and Kelvin use the same size degree. The only difference is the starting point. To change Celsius to Kelvin, you add 273.15. To change Kelvin to Celsius, you subtract 273.15.
Can temperatures in Celsius be negative?
Yes. Any temperature below 0 °C is written as a negative number, like -5 °C. This means it is colder than the freezing point of water.
Which is warmer, 30 °C or 30 °F?
30 °C is much warmer than 30 °F. 30 °C feels like a hot summer day. 30 °F is just below the freezing point of water, so it feels quite cold.