Temperature Converter
Convert temperatures between Fahrenheit, Celsius, and Kelvin online for free. Instant bidirectional conversion with formulas displayed.
How to Use
Temperature conversion is one of the most common unit conversion tasks, needed when traveling internationally, reading scientific literature, cooking with recipes from different countries, or working in engineering and science. This free online temperature converter handles Fahrenheit, Celsius, and Kelvin conversions instantly. Here is how to use it:
- Enter a temperature value in any of the three scales: Fahrenheit, Celsius, or Kelvin. You can type a number including decimals and negative values.
- See instant conversions to the other two scales. When you enter a Celsius value, the Fahrenheit and Kelvin equivalents update in real time. The same applies when entering Fahrenheit or Kelvin values.
- Review the conversion formulas displayed alongside the results. Seeing the formula helps you understand how the conversion works and verify the result independently.
- Copy any result to your clipboard for use in documents, calculations, or communications.
The bidirectional conversion design means you can type in any field and all others update automatically. There is no need to select a "from" and "to" scale — just enter a number wherever you have it, and read the result wherever you need it.
Quick Reference Temperatures
- Water freezes: 32 degrees F / 0 degrees C / 273.15 K
- Water boils: 212 degrees F / 100 degrees C / 373.15 K
- Human body temperature: 98.6 degrees F / 37 degrees C / 310.15 K
- Room temperature: 68-72 degrees F / 20-22 degrees C / 293-295 K
- Absolute zero: -459.67 degrees F / -273.15 degrees C / 0 K
- Fahrenheit-Celsius intersection: -40 degrees F = -40 degrees C = 233.15 K
About This Tool
Temperature is a measure of the average kinetic energy of particles in a substance. Three temperature scales are in common use today, each with its own history, zero point, and degree size. Understanding these scales and the relationships between them is fundamental to science, engineering, medicine, and everyday life.
The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit, a Polish-born Dutch physicist, in 1724. He calibrated his scale using three reference points: the freezing point of a brine solution (0 degrees F), the freezing point of pure water (32 degrees F), and human body temperature (originally set at 96 degrees F, later revised to 98.6 degrees F). The Fahrenheit scale places the boiling point of water at 212 degrees F, creating 180 equal divisions between freezing and boiling. Today, the Fahrenheit scale is primarily used in the United States, the Bahamas, the Cayman Islands, Liberia, Palau, the Federated States of Micronesia, and the Marshall Islands for everyday temperature measurement. Its finer degree gradations (1 degree F = 0.556 degree C) make it slightly more precise for describing ambient temperatures without decimals.
The Celsius scale, originally called "centigrade," was proposed by Swedish astronomer Anders Celsius in 1742. Celsius initially defined 0 as the boiling point and 100 as the freezing point of water, but the scale was inverted the following year by Carl Linnaeus (or possibly by Celsius's successor, Martin Stromer). The modern Celsius scale sets 0 degrees as the freezing point and 100 degrees as the boiling point of pure water at standard atmospheric pressure (101.325 kPa). This creates a clean, decimal-friendly scale that aligns naturally with the metric system. Celsius is used as the standard temperature scale in virtually every country outside the United States and is the scale used in scientific communication worldwide.
The Kelvin Scale and Absolute Zero
The Kelvin scale, named after Irish-Scottish physicist William Thomson, 1st Baron Kelvin, is the SI (International System of Units) base unit of temperature. Kelvin defined his scale in 1848 using absolute zero as the zero point, the theoretical temperature at which all molecular motion ceases. One kelvin is exactly equal in magnitude to one degree Celsius, so the Kelvin scale is simply the Celsius scale shifted by 273.15 degrees: K = C + 273.15. Unlike Fahrenheit and Celsius, the Kelvin scale does not use the degree symbol — temperatures are stated as "300 kelvins" or "300 K," not "300 degrees Kelvin." The Kelvin scale is essential in physics, chemistry, and engineering because it is an absolute scale: ratios are meaningful (200 K is genuinely twice as hot as 100 K in terms of thermal energy), which is not true for Celsius or Fahrenheit.
Why Use This Tool
Temperature conversion is a practical necessity in many contexts. Here are the most common reasons people use a temperature converter:
- International travel — When traveling between countries that use different temperature scales, understanding the local weather forecast requires conversion. An American visiting Europe needs to know that 25 degrees Celsius is a comfortable 77 degrees Fahrenheit, while a European in the US needs to know that 90 degrees Fahrenheit is a hot 32.2 degrees Celsius. Temperature conversion eliminates confusion about what clothing to pack and what activities are comfortable.
- Cooking and baking — Recipes from different countries specify oven temperatures in different scales. A British recipe calling for 180 degrees C needs to be converted to 356 degrees F for an American oven. Professional pastry recipes and scientific cooking guides often specify temperatures in Celsius for precision. Getting the conversion wrong can mean the difference between a perfectly baked cake and a burnt disaster.
- Science and engineering — Scientific literature universally uses Celsius or Kelvin. Engineers converting between imperial (Fahrenheit) and metric (Celsius) systems need accurate conversion for material specifications, process temperatures, and environmental conditions. Chemical reaction rates, material melting points, and semiconductor operating ranges are all specified in Celsius or Kelvin.
- Healthcare and medicine — Body temperature is measured in Fahrenheit in the US and Celsius elsewhere. A fever of 38.5 degrees C (101.3 degrees F) has the same clinical significance regardless of the scale, but medical professionals and patients need to convert between them when communicating across systems. Medication storage requirements (for example, "store between 2-8 degrees C") also require conversion for users accustomed to Fahrenheit.
- HVAC and home automation — Thermostat settings, furnace specifications, and air conditioning capacity are described in different scales depending on the manufacturer's origin. Smart home systems that integrate devices from different regions may display temperatures in mixed scales, requiring users to convert for consistent understanding and control.
Privacy and Accuracy
This temperature converter runs entirely in your browser. No values are sent to any server, no calculations are logged, and no account is required. The conversion formulas use exact mathematical relationships (not rounded approximations), so the results are precise to the limits of JavaScript's floating-point arithmetic (approximately 15-17 significant digits).