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Celsius (°C)

What Is Celsius (°C)?

Celsius is a scale that shows how hot or cold something is. It is used to measure temperature in most countries, for things like weather, cooking, and science.

Definition

Celsius is a unit for temperature. The scale is based on water. On this scale:

  • 0 °C is the temperature where pure water freezes.
  • 100 °C is the temperature where pure water boils, at normal air pressure.

When the number of degrees Celsius goes up, it means the temperature is getting warmer. When the number goes down, it is getting colder.

History / Origin

The Celsius scale is named after Anders Celsius, a Swedish scientist who lived in the 1700s. He wanted a clear way to measure temperature using water as a guide.

At first, his scale was the opposite of today. He put 0 at the boiling point of water and 100 at the freezing point. Other scientists later flipped the scale so that:

  • 0 °C became the freezing point.
  • 100 °C became the boiling point.

For a while, people called this scale centigrade, which means one hundred steps, because there are 100 equal steps between freezing and boiling. Today the official name is degree Celsius.

Symbol & Abbreviation

The unit has two common written forms:

  • Full name degree Celsius
  • Short form °C

The little circle before the C is called the degree sign. You write the number first, then the symbol, with no space or a small space, like this:

  • 20 °C or 20°C
  • -5 °C for five degrees below zero

Current Use Around the World

Celsius is used in most parts of everyday life in nearly all countries.

  • Weather reports Weather apps and TV forecasts show the temperature in °C in most of the world.
  • Schools and science School labs, science books, and experiments use °C to show temperatures.
  • Cooking and food Many oven settings, food labels, and recipes outside the United States give temperatures in °C.
  • Health and medicine Body temperature on medical thermometers is often written in °C, for example 37 °C.

The main countries that still use Fahrenheit in daily life are the United States and a few others. Even there, scientists and many technical fields still use Celsius or its related unit, kelvin.

Example Conversions

Here are some useful temperature values in Celsius and how they compare to Fahrenheit and kelvin.

Common temperatures

  • Freezing point of water 0 °C = 32 °F ≈ 273.15 K
  • Room temperature about 20 °C = 68 °F ≈ 293.15 K
  • Comfortable warm day about 25 °C = 77 °F ≈ 298.15 K
  • Normal human body temperature about 37 °C ≈ 98.6 °F ≈ 310.15 K
  • Boiling point of water 100 °C = 212 °F ≈ 373.15 K

How to change Celsius to Fahrenheit

Use this rule:

°F = (°C × 9 ÷ 5) + 32

Examples:

  • 0 °C → (0 × 9 ÷ 5) + 32 = 32 °F
  • 10 °C → (10 × 9 ÷ 5) + 32 = 50 °F
  • 25 °C → (25 × 9 ÷ 5) + 32 = 77 °F

How to change Fahrenheit to Celsius

Use this rule:

°C = (°F - 32) × 5 ÷ 9

Examples:

  • 32 °F → (32 – 32) × 5 ÷ 9 = 0 °C
  • 68 °F → (68 – 32) × 5 ÷ 9 = 20 °C
  • 104 °F → (104 – 32) × 5 ÷ 9 = 40 °C

How to change Celsius to kelvin

Kelvin is used in science. It starts at absolute zero, the lowest possible temperature. To change Celsius to kelvin:

K = °C + 273.15

Examples:

  • 0 °C → 273.15 K
  • 25 °C → 298.15 K

Several other temperature units are related to Celsius.

  • Fahrenheit (°F) Mainly used in the United States for weather, cooking, and body temperature. 32 °F equals 0 °C.
  • Kelvin (K) The main temperature unit in science. One kelvin change is the same size as one degree Celsius change.
  • Rankine (°R or °Ra) A temperature scale used in some engineering fields, mostly in the past, related to Fahrenheit like kelvin is related to Celsius.

Celsius and kelvin steps are the same size. Only the starting point is different. This makes it easy to change between them by adding or subtracting 273.15.

FAQs

Q What is special about 0 °C
A It is the temperature where pure water freezes at normal air pressure. It is often used as a clear line between freezing and not freezing.

Q What is special about 100 °C
A It is the temperature where pure water boils at normal air pressure. It marks the top of the basic Celsius scale.

Q Why do some countries use Fahrenheit instead of Celsius
A The United States and a few other places kept using Fahrenheit for daily life because of history and habit. However, science and many industries there also use Celsius and kelvin.

Q Can temperatures in Celsius go below 0
A Yes. Negative values show temperatures below the freezing point of water. For example, -10 °C is colder than -2 °C.

Q Is Celsius the same as centigrade
A Today they mean the same scale. Centigrade is an older name that was used because the scale has 100 parts between freezing and boiling. The official modern name is degree Celsius.

Q Which temperature unit is best for science
A Scientists often use kelvin for serious research, but because kelvin and Celsius have the same size steps, Celsius is also very common in school labs and everyday science work.

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