The Temperature Conversion Calculator instantly converts temperatures between four units: Celsius, Fahrenheit, Kelvin, and Reamur.
Enter a temperature in one unit and get conversion results for all other units. Includes conversion formulas, a reference temperature table, a visual thermometer indicator, and the history of each temperature scale.
Calculator information
📋 How to use this calculator
- Select the source temperature unit: Celsius (°C), Fahrenheit (°F), Kelvin (K), or Reaumur (°R).
- Enter the temperature value you want to convert (negative values allowed for Celsius/Fahrenheit/Reaumur).
- View the automatic conversion results displayed simultaneously in the other three units.
- Compare against the reference table (water freezing point, body temperature, water boiling point) for validation.
- Use the visual thermometer indicator to help understand the temperature context (hot/cold).
- Tip: Kelvin cannot be negative because it is an absolute scale starting from absolute zero (-273.15 °C).
🧮 Temperature Unit Conversion
°F = (°C x 9/5) + 32; K = °C + 273.15; °R = °C x 4/5; °C = (°F - 32) x 5/9.
- °C = Celsius temperature (water freezing point 0, boiling point 100 at 1 atm)
- °F = Fahrenheit temperature (water freezing point 32, boiling point 212)
- K = Kelvin temperature (absolute zero = 0 K = -273.15 °C)
- °R = Reaumur temperature (water freezing point 0, boiling point 80)
For temperature differences (delta), 1 °C = 1 K = 1.8 °F = 0.8 °R.
💡 Worked example: Converting body temperature 37 °C to Fahrenheit, Kelvin, and Reaumur
Given:- Source temperature: 37 °C (normal body temperature)
Steps:- To Fahrenheit: (37 x 9/5) + 32 = 66.6 + 32 = 98.6 °F.
- To Kelvin: 37 + 273.15 = 310.15 K.
- To Reaumur: 37 x 4/5 = 29.6 °R.
Result: A normal body temperature of 37 °C is equivalent to 98.6 °F, 310.15 K, or 29.6 °R.
❓ Frequently asked questions
Why is Fahrenheit still used in the United States?
The Fahrenheit scale was introduced by Daniel Gabriel Fahrenheit in 1724 and adopted widely in English-speaking countries. The United States and a few Caribbean nations still use it for everyday purposes, although science and medicine consistently use Celsius/Kelvin. NIST recognizes both customary and SI units, but scientific and most international communication favors Celsius.
What is absolute zero?
Absolute zero is the theoretically lowest temperature, equal to 0 K or -273.15 °C, when molecular motion stops completely. According to the third law of thermodynamics, this temperature can never be physically reached. Laboratory experiments have achieved temperatures only a billionth of a degree above absolute zero.
What is a typical average temperature in the United States?
According to NOAA data, the contiguous U.S. annual average temperature is around 53 °F (12 °C), with significant regional variation: southern states like Florida average 70 °F (21 °C) and northern states like Minnesota around 41 °F (5 °C). Extremes range from -80 °F (-62 °C) recorded in Alaska to 134 °F (57 °C) in Death Valley, California.
What is the difference between Celsius and Kelvin for scientific use?
Celsius and Kelvin have the same interval (1 °C = 1 K), but their zero points differ. Kelvin is used in physics and chemistry because, as an absolute scale, it can be applied directly in the ideal gas equation (PV=nRT), the laws of thermodynamics, and blackbody radiation. Celsius is more practical for everyday and medical measurements.
Where is the Reaumur scale still used?
The Reaumur scale was introduced by Rene-Antoine Ferchault de Reaumur in 1730. It is almost no longer used in international practice today. It occasionally appears in historical European cheese-making and liquor distillation references, but is not used for any official modern measurement. NIST and the global scientific community use Celsius and Kelvin.
📚 Sources & references
Last updated: May 11, 2026