Temperature Converter - Free Online Tool

Convert temperature units instantly. Support for 4+ units including Celsius, Fahrenheit, Kelvin. Free calculator with accurate conversions, formula, and table.

🌡️ Temperature Converter

Select your units from the lists below

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From Unit

Celsius
Symbol: °C

Fahrenheit
Symbol: °F

Kelvin
Symbol: K

Rankine
Symbol: °R

To Unit

Celsius
Symbol: °C

Fahrenheit
Symbol: °F

Kelvin
Symbol: K

Rankine
Symbol: °R

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🌡️ Temperature Converter

Temperature affects everything from cooking to scientific research. Convert between Celsius, Fahrenheit, Kelvin, and Rankine instantly. Whether you're working in research, cooking, weather forecasting, or industrial processes, our converter handles the calculations.

🌡️ About Temperature

Temperature measures the average kinetic energy of particles in a substance—basically, how hot or cold something is. Unlike length or mass, temperature needs a scale with defined reference points. The International System of Units (SI) uses the kelvin as its base unit for thermodynamic temperature, while Celsius is widely used for everyday measurements. Different regions and fields use different scales. Celsius dominates global science and most countries, while Fahrenheit remains common in the United States for weather and everyday use. Kelvin is used in scientific research where absolute temperature matters, and Rankine appears in some engineering applications. Being able to work with all these scales helps with international collaboration, manufacturing, and scientific research.

Understanding Temperature Measurement

Temperature is a fundamental physical quantity representing the thermal state of matter. In the International System of Quantities, temperature is a base dimension. Unlike other base quantities, temperature scales require defined reference points because there is no natural zero point—only an absolute zero where molecular motion theoretically ceases. In the International System of Units (SI), the kelvin serves as the base unit for thermodynamic temperature. The modern definition of the kelvin, established in 2019 by the 26th General Conference on Weights and Measures, is based on fundamental constants of nature—specifically, by fixing the numerical value of the Boltzmann constant to exactly 1.380649 × 10⁻²³ joules per kelvin. The degree Celsius is defined as having the same magnitude as the kelvin, with 0°C equal to exactly 273.15 K. This definition ensures that temperature measurements are consistent and reproducible anywhere in the world.

📜 History & Context

The history of temperature measurement dates back over two millennia, when early devices called thermoscopes could indicate relative hotness or coldness but had no numeric scale. The development of quantitative temperature scales began in the 17th and 18th centuries with the work of scientists seeking reliable reference points. In 1724, Daniel Gabriel Fahrenheit developed the Fahrenheit scale, using mercury in thermometers for the first time. He initially set 0°F to a freezing brine mixture and 96°F to human body temperature, later adjusting to 32°F for water's freezing point and 212°F for its boiling point. In 1742, Swedish astronomer Anders Celsius created the Celsius scale, but with an inverted definition: 0°C was the boiling point of water and 100°C was the freezing point. This was reversed by others, including Carl Linnaeus and Jean-Pierre Christin, to the modern form where 0°C is freezing and 100°C is boiling. Originally called "centigrade," it was officially renamed "degree Celsius" in 1948. In 1848, William Thomson (Lord Kelvin) proposed an absolute temperature scale starting at absolute zero, where molecular motion theoretically ceases. The kelvin scale became the SI base unit, initially defined by the triple point of water at 273.16 K. In 2019, the kelvin was redefined using the Boltzmann constant, making it reproducible using fundamental constants rather than a specific material property.

✨ Fun Facts

• Anders Celsius originally designed his scale with 0° as the boiling point and 100° as the freezing point of water—the opposite of how it's used today. Others reversed it shortly after his death.
• Fahrenheit was the first to use mercury in thermometers instead of alcohol, making measurements more reliable due to mercury's consistent expansion properties.
• The three temperature scales intersect at one point: −40°, where −40°C equals −40°F exactly.
• The kelvin was redefined in 2019 using the Boltzmann constant, making it the last SI base unit to move from a material-based definition to one based on fundamental constants.
• Absolute zero (0 K) is exactly −273.15°C or −459.67°F, representing the theoretical point where particles have no thermal motion.

💡 Real-World Examples

• Weather forecasting: Meteorologists use Celsius or Fahrenheit depending on the region. Converting between scales helps share international weather data and communicate with the public.
• Cooking and food safety: Recipes specify temperatures in Fahrenheit or Celsius. Food safety regulations require precise temperature monitoring during cooking, storage, and transport.
• Scientific research: Physics and chemistry experiments use Kelvin for absolute temperature measurements. Results are often converted to Celsius or Fahrenheit for reporting and communication.
• Industrial processes: Manufacturing operations monitor temperatures in various scales. Steel production uses Celsius, while HVAC systems often use Fahrenheit.
• Medical applications: Body temperature is measured in Fahrenheit or Celsius depending on location. Medical devices need to handle both scales for international use.
• Electronics and computing: Computer processors and electronic components are monitored in Celsius. Thermal management is critical for performance and preventing overheating.
• Energy production: Power plants and energy systems measure temperatures in different scales. Converting between units helps with monitoring, control, and international equipment compatibility.
• Materials science: Research on material properties uses Kelvin for absolute temperature measurements. Practical applications often report results in Celsius or Fahrenheit.

🔧 Common Applications

• Scientific research: Physics, chemistry, and materials science experiments need precise temperature measurements. Researchers use Kelvin for absolute measurements and Celsius for reporting.
• Industrial manufacturing: Process control systems monitor temperatures in various scales. Converting between units helps with equipment compatibility and international standards.
• Climate science and meteorology: Weather monitoring and climate research use temperature data from multiple sources. Converting between scales helps with global data analysis.
• Healthcare and medicine: Medical devices and patient monitoring systems use different temperature scales depending on region. Converting between units helps with international healthcare.
• Energy and power generation: Power plants, HVAC systems, and energy efficiency applications monitor temperatures across different scales. Converting between units helps with optimal operation and safety.

❓ Frequently Asked Questions

+ How do I convert Celsius to Fahrenheit?

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 (or 1.8) and add 32. The formula is: °F = (°C × 9/5) + 32. For example, 0°C equals 32°F, and 100°C equals 212°F.

+ What is the difference between Celsius and Fahrenheit?

Celsius and Fahrenheit are different temperature scales. On the Celsius scale, water freezes at 0°C and boils at 100°C. On the Fahrenheit scale, water freezes at 32°F and boils at 212°F. Celsius is used in most countries and scientific contexts, while Fahrenheit is primarily used in the United States.

+ How do I convert Fahrenheit to Celsius?

To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and multiply by 5/9. The formula is: °C = (°F - 32) × 5/9. For example, 32°F equals 0°C, and 212°F equals 100°C.

+ What is Kelvin and how does it relate to Celsius?

Kelvin is the SI base unit for temperature and uses absolute zero as its starting point. The Kelvin scale has the same degree size as Celsius, but 0 K equals -273.15°C (absolute zero). To convert Celsius to Kelvin, add 273.15. For example, 0°C equals 273.15 K, and 100°C equals 373.15 K.

+ At what temperature do Celsius and Fahrenheit have the same value?

Celsius and Fahrenheit are equal at -40 degrees. This means -40°C equals -40°F exactly. This is the only point where the two scales intersect, making it a useful reference point for conversions.