Temperature Converter: Celsius, Fahrenheit and Kelvin
Temperature Converter Guide
Temperature is measured on several different scales, and the one you see depends on where you live and what you are doing. A weather app in Paris shows Celsius, a recipe from the United States lists Fahrenheit, and a physics textbook uses Kelvin. A temperature converter lets you move between all three instantly so the number always makes sense.
Why three scales exist
Each scale was created for a different purpose, which is why all three are still in daily use.
- Celsius (°C) is the everyday metric scale used by most of the world. Water freezes at 0 and boils at 100, which makes it intuitive for weather and cooking.
- Fahrenheit (°F) is used mainly in the United States. Its degrees are smaller, so it can describe small changes in air temperature without decimals.
- Kelvin (K) is the scientific, absolute scale. It starts at absolute zero, the coldest temperature physically possible, so it never uses negative numbers.
The conversion formulas
Only three formulas are needed to move between the scales. Celsius sits in the middle, so it is usually the easiest starting point.
°F = °C × 9/5 + 32
°C = (°F − 32) × 5/9
K = °C + 273.15
Worked examples
Plugging real values into the formulas shows how they behave at familiar temperatures.
100°C = (100 × 9/5) + 32 = 212°F (boiling water)
37°C = (37 × 9/5) + 32 = 98.6°F (body temperature)
0°C = 0 + 273.15 = 273.15 K (freezing point)
A quick mental trick
When you do not need an exact answer, double the Celsius value and add 30 for a rough Fahrenheit estimate. For example, 20°C becomes about 70°F (the exact answer is 68°F), which is close enough for a weather forecast. It is also worth remembering that the two scales meet at exactly −40: −40°C is the same temperature as −40°F.
Key reference points
- Water freezes: 0°C / 32°F / 273.15 K
- Water boils at sea level: 100°C / 212°F / 373.15 K
- Comfortable room temperature: about 20–22°C / 68–72°F
- Normal body temperature: 37°C / 98.6°F
- A hot summer day: 30°C / 86°F
How to use the temperature converter online
- Enter a value in whichever scale you already know — Celsius, Fahrenheit, or Kelvin.
- The tool instantly calculates the equivalent values in the other scales.
- Copy the result you need for your recipe, forecast, or homework.
Common use cases
- Cooking: converting oven temperatures between °C and °F.
- Weather and travel: understanding forecasts when you are abroad.
- Science homework: converting to Kelvin for gas-law and physics problems.
- HVAC and appliances: reading thermostats and equipment specifications.
- Health: interpreting body-temperature readings from any thermometer.
Handy tips
- Kelvin never uses a degree symbol — you simply write “300 K”.
- The scales only cross at −40°, a useful checkpoint if a conversion ever looks wrong.
- For a clean anchor to memorize, 160°C equals exactly 320°F.
FAQ
Q: How do I convert Celsius to Fahrenheit quickly?
A: Multiply the Celsius value by 9/5 (or 1.8) and add 32. For a rough estimate in your head, double the number and add 30.
Q: What is Kelvin used for?
A: Kelvin is the standard unit in science because it starts at absolute zero, so it never uses negative numbers. It is common in physics, chemistry, and engineering calculations.
Q: At what temperature are Celsius and Fahrenheit equal?
A: At −40 degrees. −40°C and −40°F represent exactly the same temperature, and it is the only point where the two scales meet.