Temperature Converter
Temperature Conversion — Celsius, Fahrenheit, and Kelvin
Temperature is one of the most common unit conversions people need — whether you're reading a recipe from another country, checking the weather in Celsius when you're used to Fahrenheit, understanding a scientific paper, or just figuring out what to wear. The three scales serve different purposes and knowing how to move between them is genuinely useful.
The Conversion Formulas
Real-World Example
100°C (the default) is the boiling point of water at sea level:
- 100°C = 212°F = 373.15 K
Some other useful reference points:
- 0°C = 32°F — water freezes
- 20–22°C = 68–72°F — comfortable room temperature
- 37°C = 98.6°F — normal human body temperature
- −40°C = −40°F — the one point where both scales are identical
- −273.15°C = 0 K — absolute zero
The Three Temperature Scales
Celsius (°C) is the everyday temperature scale used by most of the world. It was designed around water — 0°C is the freezing point, 100°C is the boiling point (at sea level, 1 atmosphere of pressure). Developed by Anders Celsius in 1742.
Fahrenheit (°F) is used primarily in the United States and a few other countries. 32°F is freezing, 212°F is boiling. Human body temperature (98.6°F) and comfortable room temperature (72°F) are often cited as intuitive reference points in countries using this scale. Developed by Daniel Gabriel Fahrenheit in 1724.
Kelvin (K) is the SI base unit of temperature and is used in science and engineering. Unlike Celsius and Fahrenheit, Kelvin has no degree symbol — you say "373 kelvin," not "373 degrees kelvin." The scale starts at absolute zero (0 K = −273.15°C), where all molecular motion theoretically stops. One kelvin is the same size as one degree Celsius — only the starting point differs.
Why Does Water Boil at Different Temperatures at Altitude?
The 100°C / 212°F boiling point assumes standard atmospheric pressure (1 atm at sea level). At higher altitudes, air pressure is lower — water boils at a lower temperature. At 5,000 feet elevation (Denver), water boils at about 95°C / 203°F. At the top of Everest (~29,000 ft), water boils at only 70°C / 158°F — too cool to properly cook pasta or make tea. High-altitude cooking instructions exist for this reason.
Quick Mental Conversion Shortcuts
- °C to °F (rough): double it and add 30. Not exact, but close enough for weather: 20°C → 40+30 = 70°F (actual: 68°F)
- °F to °C (rough): subtract 30 and halve it. 70°F → 40÷2 = 20°C (actual: 21°C)
- The exact crossover point: −40° is the same in both Celsius and Fahrenheit — useful as a mental anchor
Frequently Asked Questions
Why does the US still use Fahrenheit?
Historical inertia, mostly. The US never completed a metric transition despite several attempts — the Metric Conversion Act of 1975 made conversion voluntary, which meant it largely didn't happen in everyday life. The result is that the US uses a mix: metric in science and medicine, imperial/Fahrenheit in everyday life. Most Americans have no intuitive sense of Celsius temperatures because they've never needed to develop one.
What is absolute zero and can it be reached?
Absolute zero (0 K = −273.15°C = −459.67°F) is the theoretical temperature at which all molecular motion ceases. It's a lower bound — you can get arbitrarily close but never actually reach it, per the third law of thermodynamics. Scientists have cooled materials to within billionths of a degree of absolute zero in laboratory settings, which enables phenomena like superconductivity and Bose-Einstein condensates.
What temperature is a fever?
Normal body temperature averages 37°C / 98.6°F, though it varies slightly by person, time of day, and measurement location. A fever is generally defined as a core temperature above 38°C / 100.4°F. Above 40°C / 104°F is considered high fever requiring medical attention. Temperature varies slightly throughout the day — lowest in the early morning, highest in late afternoon.
Why do recipes sometimes list oven temperatures in Celsius and sometimes Fahrenheit?
Recipes from the US and some older cookbooks use Fahrenheit; most international and modern recipes use Celsius. A moderate oven is around 180°C / 350°F. High oven temperature is around 220°C / 425°F. When in doubt, this converter handles the translation in seconds — and it's worth bookmarking if you cook from international recipes regularly.
Is there a temperature above which nothing can exist?
The Planck temperature (~1.416 × 10³² K) is considered the theoretical upper limit of temperature — beyond this, current physics breaks down and the laws governing matter and energy as we understand them no longer apply. This temperature existed in the first 5.4 × 10⁻⁴⁴ seconds after the Big Bang. It's about 100 million trillion trillion times hotter than the surface of the sun.