Convert between Fahrenheit, Celsius, Kelvin, Rankine, and more, instantly. Includes cooking temperatures, body temperature guide, and a real-world reference scale.
The world uses three temperature scales: Fahrenheit (US everyday use), Celsius (international standard), and Kelvin (scientific absolute scale). The US is the primary holdout on Fahrenheit, virtually every other country uses Celsius for weather and everyday temperature. For cooking, temperature conversion is a daily reality for anyone using international recipes. A French recipe calling for 180°C translates to 356°F, typically rounded to 350°F on American ovens. 200°C = 392°F ≈ 400°F. Formula: °F = (°C × 9/5) + 32. Kelvin starts at absolute zero (-273.15°C), the theoretical temperature at which all molecular motion stops. Room temperature is approximately 293-295 Kelvin. Kelvin is used in physics, astronomy, and engineering because it's an absolute scale with no negative values, making thermodynamic calculations simpler.
Temperature is a measure of the average kinetic energy of the particles in a substance. The scale you use depends on where you are in the world and what you’re measuring, everyday life, scientific research, cooking, and engineering each have their preferred systems.
Developed by Daniel Gabriel Fahrenheit in 1724, this scale set 32°F as the freezing point of water and 212°F as the boiling point at sea level, a range of 180 degrees between these two benchmarks. Fahrenheit originally calibrated his scale using a brine solution (0°F) and human body temperature (96°F, later revised to 98.6°F). The Fahrenheit scale is used primarily in the United States and a few territories for everyday temperature measurement.
Anders Celsius proposed the centigrade scale in 1742. The modern Celsius scale defines 0°C as the freezing point of water and 100°C as the boiling point at standard atmospheric pressure, a clean, intuitive range of 100 degrees. Almost every country in the world uses Celsius for everyday temperatures, and it is the preferred scale in science alongside Kelvin.
The Kelvin scale is the SI base unit of temperature and is used universally in scientific and engineering contexts. It starts at absolute zero (0 K = -273.15°C = -459.67°F), the theoretical point at which all particle motion stops. There are no negative Kelvin temperatures. Water freezes at 273.15 K and boils at 373.15 K. Importantly, you say “273 kelvin” not “273 degrees kelvin”, the word “degree” is not used with Kelvin.
The Rankine scale uses absolute zero as its starting point (like Kelvin) but uses Fahrenheit-sized degrees rather than Celsius-sized degrees. 0°R = 0 K = absolute zero. Water freezes at 491.67°R and boils at 671.67°R. Rankine is used in some engineering applications in the United States, particularly in thermodynamics and aerospace engineering that use Imperial units.
| Convert from | To Celsius | To Fahrenheit | To Kelvin |
|---|---|---|---|
| Celsius (°C) | — | (°C × 9/5) + 32 | °C + 273.15 |
| Fahrenheit (°F) | (°F − 32) × 5/9 | — | (°F + 459.67) × 5/9 |
| Kelvin (K) | K − 273.15 | (K × 9/5) − 459.67 | — |
| Rankine (°R) | (°R − 491.67) × 5/9 | °R − 459.67 | °R × 5/9 |
The United States is one of only a handful of countries that uses Fahrenheit for everyday temperatures. The metric system (including Celsius) was formally adopted in the US in 1975 through the Metric Conversion Act, but its use was made voluntary, and Fahrenheit persisted in daily life. One argument made for Fahrenheit: the 0–100°F range roughly spans the range of human experience in most inhabited climates, providing intuitive “percent of comfortable range” feedback. Most Americans know instinctively that 90°F is very hot and 20°F is very cold without calculation.
Absolute zero (0 K, -273.15°C, -459.67°F) is the lowest theoretically possible temperature. At this point, atoms have minimum vibrational motion. The third law of thermodynamics states that absolute zero can be approached but never quite reached, it would require infinite energy to remove all thermal energy from a system. Scientists have cooled matter to within a billionth of a degree above absolute zero, but the exact value remains unachievable.
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