Temperature Converter
Convert between various temperature units including Celsius, Fahrenheit, Kelvin and more
Common Temperature Conversions
Formula: (°C × 9/5) + 32 = °F
To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 (or 1.8) and add 32.
Example: 25°C = (25 × 9/5) + 32 = 77°F
Formula: (°F - 32) × 5/9 = °C
To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and multiply by 5/9.
Example: 77°F = (77 - 32) × 5/9 = 25°C
Formula: °C + 273.15 = K
To convert Celsius to Kelvin, add 273.15 to the Celsius temperature.
Example: 25°C = 25 + 273.15 = 298.15K
Temperature Conversion Reference Table
| Temperature Point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Rankine (°R) | Réaumur (°Ré) |
|---|---|---|---|---|---|
| Absolute Zero | -273.15 | -459.67 | 0 | 0 | -218.52 |
| Freezing Point of Water | 0 | 32 | 273.15 | 491.67 | 0 |
| Body Temperature | 37 | 98.6 | 310.15 | 558.27 | 29.6 |
| Boiling Point of Water | 100 | 212 | 373.15 | 671.67 | 80 |
About Temperature Units
The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI). It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale.
- Definition: In the Celsius scale, water freezes at 0°C and boils at 100°C under standard atmospheric pressure.
- Usage: The Celsius scale is used worldwide in most scientific, academic, and everyday contexts, except in the United States where Fahrenheit is still commonly used.
The Fahrenheit scale is a temperature scale based on the proposal by physicist Daniel Gabriel Fahrenheit (1686–1736), after whom the scale is named.
- Definition: In the Fahrenheit scale, water freezes at 32°F and boils at 212°F under standard atmospheric pressure.
- Usage: The Fahrenheit scale is primarily used in the United States and some Caribbean countries for everyday temperature measurement.
- History: Fahrenheit set 0°F as the freezing temperature of a brine solution and 96°F as approximate human body temperature. The scale was later recalibrated to make the freezing and boiling points of water 32°F and 212°F respectively.
The Kelvin scale is an absolute temperature scale named after the Belfast-born physicist and engineer William Thomson, 1st Baron Kelvin (1824–1907), who proposed it in 1848.
- Definition: The Kelvin scale starts at absolute zero (0K), the theoretical temperature at which all thermal motion ceases. On the Kelvin scale, water freezes at 273.15K and boils at 373.15K.
- Usage: The Kelvin is the primary unit of temperature in the physical sciences and is used in scientific contexts where absolute temperatures are required, such as in thermodynamics and astronomy.
- Note: Unlike Celsius and Fahrenheit, the Kelvin scale doesn't use the degree symbol (°). It's simply written as "K".
The Rankine scale is an absolute temperature scale named after the Scottish engineer and physicist William John Macquorn Rankine (1820–1872), who proposed it in 1859.
- Definition: Like the Kelvin scale, the Rankine scale starts at absolute zero. However, it uses the Fahrenheit degree as its unit increment rather than the Celsius degree. Water freezes at 491.67°R and boils at 671.67°R.
- Usage: The Rankine scale is mainly used in some engineering systems in the United States, particularly in the field of thermodynamics.
- Relationship: Rankine (°R) = Fahrenheit (°F) + 459.67, similar to how Kelvin (K) = Celsius (°C) + 273.15.
The Réaumur scale is a temperature scale named after René Antoine Ferchault de Réaumur (1683–1757), who first proposed it in 1730.
- Definition: On the Réaumur scale, the freezing point of water is 0 degrees Réaumur (°Ré), and the boiling point is 80°Ré.
- Usage: The Réaumur scale is now rarely used. Historically, it was widely used in Europe, particularly in France, Germany, and Russia, during the 18th and 19th centuries for measuring the temperature of air, solutions, and spirits.
- Historical Importance: The Réaumur scale was once important in the alcohol industry. Many older European cookbooks and recipes for brewing and winemaking used the Réaumur scale.
Frequently Asked Questions
The temperature where the Celsius and Fahrenheit scales have the same numerical value is -40 degrees. That is, -40°C = -40°F. This can be verified by solving the equation: (F - 32) × 5/9 = C, where C = F, which gives F = -40.
Absolute zero is the lowest possible temperature where all molecular motion ceases. It is defined as 0 Kelvin (0K), which is equivalent to -273.15°C or -459.67°F. It is important in physics and thermodynamics because it represents the theoretical lower limit of temperature. According to the third law of thermodynamics, it is impossible to reach absolute zero through any physical process, although scientists have achieved temperatures very close to it in laboratory settings.
To convert from Kelvin to Celsius, subtract 273.15 from the Kelvin temperature: °C = K - 273.15
To convert from Kelvin to Fahrenheit, first convert to Celsius and then to Fahrenheit: °F = (K - 273.15) × 9/5 + 32
For example, to convert 300K to Celsius: 300K - 273.15 = 26.85°C
And to convert 300K to Fahrenheit: (300K - 273.15) × 9/5 + 32 = 26.85°C × 9/5 + 32 = 80.33°F
Different temperature scales were developed at different times and in different contexts for varying purposes:
- Celsius: Developed for scientific use with a convenient scale based on water's freezing and boiling points.
- Fahrenheit: Originally developed with reference points that were relevant at the time, including human body temperature and freezing salt water.
- Kelvin: Developed for scientific applications requiring an absolute temperature scale that starts at absolute zero.
Today, different scales persist due to historical precedent, cultural factors, and specific scientific and engineering needs. For example, Celsius is used in most of the world for everyday purposes, Fahrenheit persists in the U.S. due to cultural inertia, and Kelvin is essential for scientific applications where absolute temperature is required.
The average normal human body temperature is:
- Celsius: 37°C
- Fahrenheit: 98.6°F
- Kelvin: 310.15K
- Rankine: 558.27°R
- Réaumur: 29.6°Ré
However, it's important to note that "normal" body temperature can vary by person, age, time of day, and measurement method. Recent studies suggest that the average human body temperature may actually be slightly lower than these traditional values, closer to 36.5-36.9°C (97.7-98.4°F).