Convert between Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur temperature scales with precision. Get instant results with exact formulas.
The most widely used temperature scale globally, based on water's freezing (0°C) and boiling (100°C) points at standard pressure.
Primarily used in the United States, this scale sets water's freezing point at 32°F and boiling point at 212°F.
The SI unit for temperature, starting at absolute zero. Used in scientific applications worldwide.
A temperature converter is a tool that allows you to quickly convert between different temperature scales including Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur. Whether you need to convert Celsius to Fahrenheit for weather reports, Fahrenheit to Celsius for cooking, or Celsius to Kelvin for scientific calculations, this guide provides exact formulas and practical examples for all temperature conversions.
Temperature scales measure the degree of heat or cold. Different scales were developed at different times in history for various purposes. Today, five main temperature scales are in use:
Celsius (°C) – Used by most countries worldwide, based on water's properties
Fahrenheit (°F) – Primarily used in the United States
Kelvin (K) – The SI unit for temperature, used in scientific applications
Rankine (°R) – An absolute scale based on Fahrenheit, used in engineering
Réaumur (°Ré) – A historical scale still used in some specialized applications
The Celsius scale, originally called centigrade, was developed by Swedish astronomer Anders Celsius in 1742. Initially, Celsius set 0° at water's boiling point and 100° at water's freezing point. After his death, the scale was inverted to its current form.
Celsius is now the standard temperature scale in almost every country except the United States. It's part of the metric system and is used in weather forecasting, cooking, medicine, and daily life across the globe. The scale is intuitive because it's based on water's physical properties at standard atmospheric pressure: water freezes at 0°C and boils at 100°C.
The Fahrenheit scale was proposed by German physicist Daniel Gabriel Fahrenheit in 1724. Fahrenheit originally set 0°F as the temperature of a mixture of ice, water, and ammonium chloride (a freezing mixture), 32°F as the freezing point of water, and 96°F as human body temperature (later adjusted to 98.6°F).
The Fahrenheit scale is primarily used in the United States, its territories, and a few Caribbean nations. It provides finer granularity than Celsius—there are 180 degrees between water's freezing and boiling points in Fahrenheit versus 100 degrees in Celsius. Some argue this makes Fahrenheit more precise for everyday temperature discussions.
The coexistence of Celsius and Fahrenheit stems from historical development and regional adoption. Most countries adopted the metric system, including Celsius, during the 19th and 20th centuries. The United States, however, retained its traditional measurement systems, including Fahrenheit. Both scales are equally valid—they simply use different reference points and increments to measure the same physical property: thermal energy.
Formula: °F = (°C × 9/5) + 32
Example 1: 25°C × 9/5 + 32 = 77°F
Example 2: 100°C × 9/5 + 32 = 212°F (boiling point of water)
Example 3: -40°C × 9/5 + 32 = -40°F (the temperature where both scales meet)
To convert Celsius to Fahrenheit, multiply by 1.8 (or 9/5) and add 32. This accounts for both the different degree sizes and the different zero points.
Formula: °C = (°F - 32) × 5/9
Example 1: (68°F - 32) × 5/9 = 20°C (comfortable room temperature)
Example 2: (32°F - 32) × 5/9 = 0°C (freezing point of water)
Example 3: (98.6°F - 32) × 5/9 = 37°C (normal human body temperature)
To convert Fahrenheit to Celsius, subtract 32 and then multiply by 5/9 (or divide by 1.8).
Formula: K = °C + 273.15
Example 1: 0°C + 273.15 = 273.15 K (water's freezing point)
Example 2: 25°C + 273.15 = 298.15 K (typical room temperature)
Example 3: 100°C + 273.15 = 373.15 K (water's boiling point)
The Kelvin scale uses the same degree size as Celsius but starts at absolute zero. Simply add 273.15 to convert Celsius to Kelvin.
Formula: °C = K - 273.15
Example 1: 273.15 K - 273.15 = 0°C
Example 2: 300 K - 273.15 = 26.85°C
Example 3: 0 K - 273.15 = -273.15°C (absolute zero)
Formula: K = (°F - 32) × 5/9 + 273.15
Example 1: (77°F - 32) × 5/9 + 273.15 = 298.15 K
Example 2: (32°F - 32) × 5/9 + 273.15 = 273.15 K
Formula: °F = (K - 273.15) × 9/5 + 32
Example 1: (298.15 K - 273.15) × 9/5 + 32 = 77°F
Example 2: (373.15 K - 273.15) × 9/5 + 32 = 212°F
The Kelvin scale was developed by William Thomson, 1st Baron Kelvin, in 1848. It's named in his honor and is the SI (International System of Units) base unit for temperature. Unlike Celsius and Fahrenheit, Kelvin is an absolute temperature scale—it starts at absolute zero, the theoretical temperature at which all molecular motion ceases.
Kelvin uses the same degree size as Celsius, making conversion between them straightforward. However, Kelvin has no negative values because absolute zero (0 K) is the lowest theoretically possible temperature. This makes Kelvin ideal for scientific calculations, particularly in physics and chemistry, where absolute temperatures are essential.
Kelvin is universally used in scientific research, particularly in physics, chemistry, astronomy, and materials science. It's essential for:
Thermodynamics: Laws of thermodynamics require absolute temperature scales
Cryogenics: Studying materials at extremely low temperatures near absolute zero
Space science: Measuring temperatures of celestial bodies and cosmic phenomena
Spectroscopy: Analyzing electromagnetic radiation and atomic properties
Climate science: Precise temperature measurements for atmospheric studies
The Rankine scale was proposed by Scottish engineer and physicist William John Macquorn Rankine in 1859. Like Kelvin, Rankine is an absolute temperature scale starting at absolute zero. However, it uses the same degree size as Fahrenheit rather than Celsius.
Fahrenheit to Rankine: °R = °F + 459.67
Celsius to Rankine: °R = (°C + 273.15) × 9/5
Kelvin to Rankine: °R = K × 9/5
Rankine is primarily used in engineering fields in the United States, particularly in:
Thermodynamic engineering: Heat engines, refrigeration cycles, and power plants
Aerospace engineering: Propulsion systems and thermal analysis
Chemical engineering: Process calculations requiring absolute temperatures
HVAC systems: Heating, ventilation, and air conditioning design
Rankine allows engineers who work primarily with Fahrenheit to perform thermodynamic calculations without converting to Kelvin. Absolute zero is 0°R, which equals -459.67°F.
The Réaumur scale was introduced by French scientist René Antoine Ferchault de Réaumur in 1730. It sets water's freezing point at 0°Ré and boiling point at 80°Ré, creating an 80-degree span between these reference points.
Celsius to Réaumur: °Ré = °C × 4/5
Réaumur to Celsius: °C = °Ré × 5/4
Fahrenheit to Réaumur: °Ré = (°F - 32) × 4/9
Réaumur to Fahrenheit: °F = °Ré × 9/4 + 32
The Réaumur scale was widely used in Europe, particularly in France, Germany, and Russia, during the 18th and 19th centuries. By the late 19th century, most countries transitioned to Celsius. However, Réaumur persisted in some regions well into the 20th century.
While largely obsolete, the Réaumur scale still appears in specific contexts:
Cheese making: Some traditional European cheese recipes specify temperatures in Réaumur
Sugar production: Certain sugar refining processes in Europe use Réaumur
Historical documents: Scientific and technical records from the 18th and 19th centuries
Thermometer collections: Antique thermometers often display Réaumur scales
Italian food industries: Some traditional Italian food production still references Réaumur
| Reference Point | Celsius | Fahrenheit | Kelvin | Rankine | Réaumur |
|---|---|---|---|---|---|
| Absolute Zero | -273.15°C | -459.67°F | 0 K | 0°R | -218.52°Ré |
| Water Freezing Point | 0°C | 32°F | 273.15 K | 491.67°R | 0°Ré |
| Room Temperature | 20°C | 68°F | 293.15 K | 527.67°R | 16°Ré |
| Human Body Temperature | 37°C | 98.6°F | 310.15 K | 558.27°R | 29.6°Ré |
| Water Boiling Point | 100°C | 212°F | 373.15 K | 671.67°R | 80°Ré |
| From | To | Formula |
|---|---|---|
| °C | °F | °F = °C × 9/5 + 32 |
| °F | °C | °C = (°F - 32) × 5/9 |
| °C | K | K = °C + 273.15 |
| K | °C | °C = K - 273.15 |
| °F | K | K = (°F - 32) × 5/9 + 273.15 |
| K | °F | °F = (K - 273.15) × 9/5 + 32 |
| °F | °R | °R = °F + 459.67 |
| °R | °F | °F = °R - 459.67 |
| K | °R | °R = K × 9/5 |
| °R | K | K = °R × 5/9 |
| °C | °Ré | °Ré = °C × 4/5 |
| °Ré | °C | °C = °Ré × 5/4 |
Multiply Celsius by 9/5 (or 1.8), then add 32. Formula: °F = (°C × 9/5) + 32. Example: 20°C × 9/5 + 32 = 68°F.
Subtract 32 from Fahrenheit, then multiply by 5/9. Formula: °C = (°F - 32) × 5/9. Example: (72°F - 32) × 5/9 = 22.2°C.
A quick mental approximation: double the Celsius temperature and add 30. This gives you a rough Fahrenheit value. For example, 20°C: 20 × 2 + 30 = 70°F (actual: 68°F). For precise conversions, use the exact formula.
Add 273.15 to the Celsius temperature. Formula: K = °C + 273.15. Example: 25°C + 273.15 = 298.15 K.
Subtract 273.15 from the Kelvin temperature. Formula: °C = K - 273.15. Example: 300 K - 273.15 = 26.85°C.
No. Kelvin is an absolute temperature scale starting at absolute zero (0 K), the lowest theoretically possible temperature. There are no negative Kelvin values.
-40 degrees is the same in both Celsius and Fahrenheit. -40°C = -40°F. This is the only temperature where both scales intersect.
The United States adopted Fahrenheit before the metric system became widespread. When most countries transitioned to metric (including Celsius) in the 19th and 20th centuries, the US retained its traditional measurement systems due to established infrastructure, economic costs of conversion, and cultural preference.
All temperature scales are equally accurate—they're just different ways to measure the same physical property. The choice of scale depends on regional convention and application. Scientists prefer Kelvin for absolute measurements, while Celsius and Fahrenheit are used for everyday purposes in different regions.
Absolute zero, the lowest possible temperature, is: 0 K (Kelvin), -273.15°C (Celsius), -459.67°F (Fahrenheit), 0°R (Rankine), and -218.52°Ré (Réaumur).
Normal room temperature (approximately 20-22°C) is: 20°C = 68°F = 293.15 K = 527.67°R = 16°Ré.
Subtract 32 from Fahrenheit, multiply by 5/9, then add 273.15. Formula: K = (°F - 32) × 5/9 + 273.15. Example: (77°F - 32) × 5/9 + 273.15 = 298.15 K.
Rankine is an absolute temperature scale used primarily in engineering applications in the United States. It's particularly useful in thermodynamics, aerospace engineering, and chemical engineering when working with Fahrenheit-based systems that require absolute temperatures.
The Réaumur scale is largely obsolete but still appears in specialized contexts such as traditional European cheese making, sugar refining, and historical scientific documents. Most modern applications have switched to Celsius or Fahrenheit.
Normal human body temperature is approximately: 37°C = 98.6°F = 310.15 K = 558.27°R = 29.6°Ré.
At standard atmospheric pressure, water boils at: 100°C = 212°F = 373.15 K = 671.67°R = 80°Ré.
Yes, temperature converters are essential for cooking, especially when using recipes from different countries. Oven temperatures, meat internal temperatures, and candy-making temperatures all require accurate conversions between Celsius and Fahrenheit.
They are the same scale. The scale was originally called "centigrade" (meaning 100 degrees) but was officially renamed "Celsius" in 1948 to honor Anders Celsius, who developed the scale.
Different temperature scales were developed at different times in history by various scientists, each using different reference points. Some scales were designed for everyday use (Celsius, Fahrenheit), while others were created for scientific purposes (Kelvin, Rankine). Regional preferences and historical adoption patterns explain why multiple scales persist today.
If the converter uses standard conversion formulas, it will be highly accurate, typically to several decimal places. This precision is suitable for virtually all practical applications from cooking to scientific calculations.