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Temperature Converter

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Temperature Converter — Convert Celsius, Fahrenheit, Kelvin & More

Our free online Temperature Converter lets you instantly convert between all major temperature scales — Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, and the triple point of water. Whether you need to convert Celsius to Fahrenheit, Kelvin to Celsius, or Fahrenheit to Kelvin, this tool delivers instant and highly accurate results without any installation.

Temperature is a fundamental physical quantity that measures how hot or cold something is. Unlike most unit conversions, temperature conversions involve offset formulas rather than simple multiplication. The main scales are:

  • Celsius (°C): The metric system standard. Water freezes at 0°C and boils at 100°C at standard pressure.
  • Fahrenheit (°F): Used primarily in the US. Water freezes at 32°F and boils at 212°F.
  • Kelvin (K): The SI base unit of temperature. Absolute zero is 0 K (−273.15°C). Used in science and engineering.
  • Rankine (°R): An absolute temperature scale using Fahrenheit-sized degrees. Used in some US engineering fields.
  • Réaumur (°Ré): A historical European scale where water freezes at 0°Ré and boils at 80°Ré.

All conversions use exact mathematical formulas, making results reliable for science, cooking, meteorology, medicine, and engineering.

Common Temperature Conversion Reference

Here are the most frequently used temperature conversions for quick reference:

  • 0°C = 32°F = 273.15 K (water freezing point)
  • 100°C = 212°F = 373.15 K (water boiling point at sea level)
  • 37°C = 98.6°F = 310.15 K (normal human body temperature)
  • 20°C = 68°F = 293.15 K (typical room temperature)
  • −40°C = −40°F = 233.15 K (Celsius and Fahrenheit are equal here)
  • Absolute zero: −273.15°C = −459.67°F = 0 K = 0°R
  • To convert °C to °F: multiply by 9/5, then add 32
  • To convert °F to °C: subtract 32, then multiply by 5/9

Frequently Asked Questions — Temperature Converter

Question: How do I use the Temperature Converter?

Answer: Select the scale you are converting from in the left list and the scale to convert to in the right list, then type your value. The result appears instantly. Temperature accepts negative numbers and decimals.

Question: How do I convert Celsius to Fahrenheit?

Answer: Use the formula: °F = (°C × 9/5) + 32. For example, 25°C = (25 × 9/5) + 32 = 45 + 32 = 77°F. You can also use the converter above for an instant result.

Question: How do I convert Fahrenheit to Celsius?

Answer: Use the formula: °C = (°F − 32) × 5/9. For example, 98.6°F = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37°C (normal human body temperature).

Question: What is the difference between Celsius and Kelvin?

Answer: Celsius and Kelvin use the same degree size but differ in their zero point. 0 K is absolute zero (the coldest possible temperature), which equals −273.15°C. To convert: K = °C + 273.15.

Question: What is absolute zero?

Answer: Absolute zero is the lowest theoretically possible temperature, defined as 0 K, −273.15°C, or −459.67°F. At this temperature, all thermal motion of particles would cease.

Question: At what temperature are Celsius and Fahrenheit equal?

Answer: Celsius and Fahrenheit are exactly equal at −40 degrees: −40°C = −40°F. This is the only point where both scales give the same reading.

Question: What is the Rankine scale?

Answer: Rankine (°R) is an absolute temperature scale that uses Fahrenheit-sized degrees, starting from absolute zero. 0 K = 0°R; to convert: °R = (°F + 459.67). It is used in some US thermodynamic engineering applications.

Question: What is normal human body temperature in Fahrenheit and Celsius?

Answer: Normal human body temperature is approximately 37°C (98.6°F) or 310.15 K. However, normal body temperature can range from about 36.1°C (97°F) to 37.2°C (99°F) depending on the person and time of day.

Question: Why does temperature conversion use formulas instead of simple multiplication?

Answer: Unlike length or weight conversions, temperature scales have different zero points (offsets). Celsius and Fahrenheit start at different values for the same physical state (e.g., water freezing), so you must account for both the scale difference and the offset when converting.