Celsius (°C)
Most common temperature scale worldwide. Based on water freezing at 0°C and boiling at 100°C at standard pressure. Also called Centigrade.
Common uses: Weather, cooking, science, everyday temperature, thermometers, medical.
Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin, Rankine, Reaumur, and other temperature scales with scientific precision.
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Temperature Scales Explained
Fahrenheit (°F)
Temperature scale primarily used in the USA. Water freezes at 32°F and boils at 212°F. Formula: °F = (°C × 9/5) + 32.
Common uses: US weather, US cooking recipes, US medical (body temperature), everyday conversation in USA.
Kelvin (K)
SI unit of absolute temperature. 0 K is absolute zero (coldest possible temperature). Water freezes at 273.15 K and boils at 373.15 K.
Common uses: Science, physics, astronomy, chemistry, thermodynamics, color temperature in lighting.
Rankine (°R)
Absolute temperature scale using Fahrenheit increments. 0°R = absolute zero. °R = °F + 459.67. Rarely used today.
Common uses: Some engineering applications, thermodynamic calculations, historical scientific work.
Reaumur (°r or °Re)
Historical temperature scale. Water freezes at 0°r and boils at 80°r. °r = °C × 4/5. Largely obsolete, rarely used.
Common uses: Historical scientific data, some older European instruments, rarely in modern applications.
Triple Point of Water
Precise reference point where ice, liquid water, and water vapor coexist. Set at exactly 273.16 K and 0.01°C. Used to define Kelvin scale.
Common uses: Scientific precision, calibration of thermometers, fundamental physics reference.
Common Temperature Conversions
- Absolute Zero: 0 K = -273.15°C = -459.67°F
- Water Freezes: 273.15 K = 0°C = 32°F = 491.67°R
- Room Temperature: 293.15 K = 20°C = 68°F
- Body Temperature: 310.15 K = 37°C = 98.6°F
- Water Boils: 373.15 K = 100°C = 212°F = 671.67°R
- Sun's Surface: ~5778 K = ~5505°C = ~9941°F
- Tungsten Melts: 3695 K = 3422°C = 6192°F
Key Differences Between Temperature Scales
- Celsius & Fahrenheit: Different zero points and scale intervals (9/5 ratio)
- Kelvin & Rankine: Absolute scales starting at true zero (absolute zero)
- Scale intervals:
- Celsius & Kelvin: 1 degree change = same magnitude
- Fahrenheit & Rankine: Smaller degree increments (5/9 of Celsius)
- Reaumur: 4/5 of Celsius increments
- Zero point significance:
- Absolute zero: 0 K (physically meaningful)
- Celsius zero: Water freezing point (arbitrary but practical)
- Fahrenheit zero: Historical arbitrary point
Cooking Temperature Guide
- Freezer Storage: -18°C (0°F)
- Refrigerator: 4°C (39°F)
- Room Temperature: 20-25°C (68-77°F)
- Warm (hand comfort): ~37°C (98.6°F)
- Chicken Internal: 75°C (165°F)
- Beef Medium: 63°C (145°F)
- Pork Safe: 71°C (160°F)
- Boiling Water: 100°C (212°F)
- Oven (moderate): 180°C (350°F)
- Oven (hot): 200-220°C (400-425°F)
Weather Temperature Reference
- Arctic conditions: Below -40°C (-40°F)
- Very cold: -20°C (-4°F)
- Freezing: 0°C (32°F)
- Cold: 5-10°C (41-50°F)
- Cool: 10-15°C (50-59°F)
- Mild: 15-20°C (59-68°F)
- Comfortable: 20-25°C (68-77°F)
- Warm: 25-30°C (77-86°F)
- Hot: 30-35°C (86-95°F)
- Very hot: Above 40°C (104°F)
- Record high (Earth): 54.0°C (129.2°F) - Death Valley
- Record low (Earth): -89.2°C (-128.6°F) - Antarctica
Temperature Conversion Formulas
- Celsius to Fahrenheit: °F = (°C × 9/5) + 32
- Fahrenheit to Celsius: °C = (°F - 32) × 5/9
- Celsius to Kelvin: K = °C + 273.15
- Kelvin to Celsius: °C = K - 273.15
- Fahrenheit to Rankine: °R = °F + 459.67
- Kelvin to Rankine: °R = K × 9/5
- Celsius to Reaumur: °r = °C × 4/5
- Reaumur to Celsius: °C = °r × 5/4
Why Multiple Temperature Scales?
- Historical development: Different scales developed independently in different countries/regions
- Fahrenheit: Designed for better precision with water's freezing/boiling in smaller increments
- Celsius: Based on decimal system (0-100 for water transitions), adopted internationally
- Kelvin: Scientific standard based on absolute zero and thermodynamic principles
- Regional persistence: US continues using Fahrenheit for historical and practical reasons
- Modern trend: Global scientific work uses Kelvin and Celsius exclusively
- Reaumur/Rankine: Largely historical, rarely used except in specialized applications