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Temperature is a measure of thermal energy and heat. Different temperature scales were developed throughout history based on different reference points and scientific needs. The three most common temperature scales are Celsius, Fahrenheit, and Kelvin.
Watch this video tutorial to learn how to convert between Celsius, Fahrenheit, and Kelvin temperature scales with easy-to-follow explanations.
Developed by: Anders Celsius in 1742
Reference points: 0°C (freezing point of water) and 100°C (boiling point of water) at standard atmospheric pressure
Usage: Most countries worldwide, scientific applications, daily temperature measurements
Notable temperatures:
• 37°C: Average human body temperature
• -78.5°C: Dry ice (solid CO₂)
• -196°C: Liquid nitrogen
Developed by: Daniel Gabriel Fahrenheit in 1724
Reference points: Originally based on the freezing temperature of brine (0°F) and approximate human body temperature (96°F), later adjusted so water freezes at 32°F and boils at 212°F
Usage: United States, Belize, Palau, the Bahamas, and a few other countries
Notable temperatures:
• 98.6°F: Average human body temperature
• 32°F: Freezing point of water
• 68°F: Room temperature
Developed by: William Thomson (Lord Kelvin) in 1848
Reference points: 0K is absolute zero (the theoretical absence of all thermal energy). No negative values are possible.
Usage: Scientific research, physics, chemistry, thermodynamics
Notable temperatures:
• 273.15K: Freezing point of water
• 373.15K: Boiling point of water
• 2.7K: Temperature of cosmic microwave background radiation
From | To | Formula |
|---|---|---|
| Celsius (°C) | Fahrenheit (°F) | °F = (°C × 9/5) + 32 |
| Celsius (°C) | Kelvin (K) | K = °C + 273.15 |
| Fahrenheit (°F) | Celsius (°C) | °C = (°F - 32) × 5/9 |
| Fahrenheit (°F) | Kelvin (K) | K = (°F - 32) × 5/9 + 273.15 |
| Kelvin (K) | Celsius (°C) | °C = K - 273.15 |
| Kelvin (K) | Fahrenheit (°F) | °F = (K - 273.15) × 9/5 + 32 |
Description | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute Zero | -273.15 | -459.67 | 0 |
| Freezing Point of Water | 0 | 32 | 273.15 |
| Average Room Temperature | 20 | 68 | 293.15 |
| Normal Human Body Temperature | 37 | 98.6 | 310.15 |
| Boiling Point of Water | 100 | 212 | 373.15 |
| Surface of the Sun | 5,505 | 9,941 | 5,778 |
Developed by William John Macquorn Rankine in 1859, the Rankine scale is to Fahrenheit what Kelvin is to Celsius—an absolute temperature scale.
Key points:
• 0°R is absolute zero
• 459.67°R equals 0°F
• Conversion from Fahrenheit: °R = °F + 459.67
• Used primarily in some engineering fields in the US
Developed by René Antoine Ferchault de Réaumur in 1730, this scale was widely used in Europe, especially in France, Germany, and Russia, until the mid-19th century.
Key points:
• 0°Ré is the freezing point of water
• 80°Ré is the boiling point of water
• Conversion from Celsius: °Ré = °C × 0.8
• Largely obsolete today but still found on some antique thermometers
The development of temperature scales reflects our evolving understanding of heat and thermodynamics:
Galen proposes a primitive temperature scale with four degrees of heat and cold.
Galileo Galilei invents the thermoscope, the first primitive device to show temperature changes.
Daniel Gabriel Fahrenheit introduces the mercury thermometer and the Fahrenheit scale.
Anders Celsius proposes the Celsius scale (initially inverted with 0° as boiling and 100° as freezing).
Lord Kelvin proposes an absolute temperature scale, later named the Kelvin scale.
The International System of Units (SI) adopts the Kelvin as its base unit of thermodynamic temperature.
Celsius is used globally for weather forecasts, cooking, and general temperature measurements. Fahrenheit remains common in the US for weather, body temperature, and household settings.
Kelvin is essential in physics and chemistry, where absolute temperature is needed for gas laws, thermodynamics, and quantum mechanics. Celsius is common in biochemistry and environmental science.
All scales find use in industry depending on location and application. Manufacturing processes, materials testing, and quality control may use different scales based on industry standards or regional preferences.
• When working with scientific data, Kelvin is the standard unit.
• Weather forecasts use Celsius in most countries and Fahrenheit in the US.
• Negative temperatures exist in both Celsius and Fahrenheit but not in Kelvin.
• Remember that -40°C equals -40°F - the only point where these scales meet.