What is Celsius?
Celsius is a temperature scale used widely in the UK and around the world. Water freezes at 0°C and boils at 100°C under standard conditions.
Celsius is a temperature scale where 0°C is the freezing point of water and 100°C is the boiling point of water under standard atmospheric pressure.
It is the main everyday temperature scale used in the UK for weather, cooking, heating, cooling and many scientific or practical measurements. You may also need to convert Celsius to Fahrenheit or Kelvin.
Why Celsius matters
Celsius is the temperature unit most UK users see in weather forecasts, thermostats, recipes, fridges, freezers and household appliances.
It is also useful when reading international recipes, travel weather, product manuals and older content that may show Fahrenheit instead.
Key Celsius reference points
These common reference points make Celsius easier to understand and convert.
| Celsius | Fahrenheit | Common meaning |
|---|---|---|
| 0°C | 32°F | Water freezes |
| 10°C | 50°F | Cool outdoor temperature |
| 20°C | 68°F | Comfortable room temperature |
| 37°C | 98.6°F | Approximate normal body temperature |
| 100°C | 212°F | Water boils under standard conditions |
Celsius conversion formulas
Celsius, Fahrenheit and Kelvin use different starting points and step sizes, so temperature conversions need formulas rather than a single simple multiplier.
Celsius = (Fahrenheit − 32) × 5 ÷ 9
Kelvin = Celsius + 273.15
Celsius = Kelvin − 273.15
Use the Temperature Converter if you want the answer instantly without doing the formula manually.
Celsius vs Fahrenheit
Celsius is common in the UK and most of the world. Fahrenheit is still often used in the United States, older recipes and some imported appliance instructions.
| Scale | Water freezes | Water boils | Common use |
|---|---|---|---|
| Celsius | 0°C | 100°C | UK weather, cooking, appliances and everyday measurements |
| Fahrenheit | 32°F | 212°F | US weather, some recipes and older temperature references |
| Kelvin | 273.15 K | 373.15 K | Science and technical temperature calculations |
Celsius vs Kelvin
Celsius and Kelvin use the same size degree step, but they start from different zero points. Kelvin starts at absolute zero, while Celsius is aligned around the freezing and boiling points of water.
That makes Kelvin useful in science, while Celsius is easier for everyday temperatures.
20°C = 293.15 K
100°C = 373.15 K
Common UK uses
Celsius appears in lots of everyday UK situations.
- Weather: forecasts usually show air temperature in degrees Celsius.
- Cooking: UK recipes commonly use Celsius, often with separate fan oven or gas mark guidance.
- Home heating: thermostats are normally set in Celsius.
- Food storage: fridge and freezer guidance usually uses Celsius.
- Health: body temperature readings are often shown in Celsius.
Celsius conversion examples
| Question | Calculation | Answer |
|---|---|---|
| What is 20°C in Fahrenheit? | (20 × 9 ÷ 5) + 32 | 68°F |
| What is 0°C in Fahrenheit? | (0 × 9 ÷ 5) + 32 | 32°F |
| What is 100°C in Fahrenheit? | (100 × 9 ÷ 5) + 32 | 212°F |
| What is 25°C in Kelvin? | 25 + 273.15 | 298.15 K |
Rounding Celsius conversions
For weather, home use and everyday comparisons, rounding to the nearest whole degree is often enough. For scientific, medical or technical use, keep more decimal places where required.
For example, 68°F converts exactly to 20°C, but 70°F converts to about 21.1°C. In everyday conversation, that might be rounded to 21°C.
Quick answers
| Question | Answer |
|---|---|
| What does Celsius measure? | Temperature. |
| What is 0°C in Fahrenheit? | 32°F. |
| What is 20°C in Fahrenheit? | 68°F. |
| What is 100°C in Fahrenheit? | 212°F. |
FAQs
What is Celsius used for?
Celsius is used to measure temperature. In the UK it is common for weather, cooking, heating, appliances and general everyday temperature readings.
How do you convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5, then add 32.
How do you convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply the result by 5/9.
Is Celsius the same as Kelvin?
No. Celsius and Kelvin use the same step size, but Kelvin starts at absolute zero. To convert Celsius to Kelvin, add 273.15.
Sources
Conversion formulas use standard temperature relationships: °F = (°C × 9/5) + 32, °C = (°F − 32) × 5/9, and K = °C + 273.15.