Temperature Converter

How to convert between temperature scales?

Temperature conversion requires understanding three different reference systems. Here's exactly how to get precise results:

• Enter your temperature value in the input field. You can type whole numbers like 100, decimals like 36.6, or negative values like -40.
• Select your source scale from the first dropdown: Celsius (°C) for most of the world, Fahrenheit (°F) primarily used in the United States, or Kelvin (K) for scientific calculations.
• Choose your target scale from the second dropdown. The result appears instantly — for example, entering 100°C shows 212°F and 373.15K simultaneously.
• Use the Swap button to reverse the direction without re-entering data. This is particularly useful when comparing body temperature across scales: 98.6°F converts to 37°C or 310.15K.
• Copy any result using the copy icon. Kelvin values are displayed without a degree symbol per SI convention, while Celsius and Fahrenheit include °.

Why three temperature scales exist and when each matters

Celsius was designed around water's phase changes at standard atmospheric pressure: 0°C for freezing and 100°C for boiling. This made it intuitive for weather, cooking, and everyday use across Europe and eventually the world. Fahrenheit, created by Daniel Gabriel Fahrenheit in 1724, uses 32°F for water's freezing point and 212°F for boiling — giving a 180-degree range instead of Celsius's 100 degrees. The finer granularity meant early thermometers could distinguish smaller temperature differences without decimals. Fahrenheit persists in the US partly due to historical inertia and partly because human comfort ranges map conveniently to 0-100°F (roughly -18°C to 38°C). Kelvin, named after Lord Kelvin, starts at absolute zero (-273.15°C) where molecular motion theoretically stops. It has no degree symbol and no negative values, making it essential for thermodynamics equations like PV=nRT. In chemistry labs, a reaction requiring 298K must not be confused with 298°C — that would be 24.85°C instead of 298°C, a critical distinction for experimental reproducibility.

The unique crossover point and other notable temperatures

• -40° is the only temperature where Celsius and Fahrenheit read identically: -40°C = -40°F. Below this point, Fahrenheit reads higher; above it, Celsius reads higher.
• Absolute zero (0K / -273.15°C / -459.67°F) represents the theoretical limit where all thermal motion ceases. Scientists have reached within billionths of a degree but never actually achieved it.
• Human body temperature averages 37°C (98.6°F), though recent studies suggest 36.5-37.5°C is normal depending on measurement site and time of day.
• Room temperature varies by standard: ISO 1 defines it as 20°C (68°F), ASHRAE uses 22-24°C (72-75°F), and many people consider 25°C (77°F) comfortable.
• Water boils at 100°C/212°F at sea level, but at 90°C (194°F) in Denver (1600m elevation) due to lower atmospheric pressure — important for cooking and industrial processes.