Celsius to Fahrenheit Conversion — Formula, Chart & Quick Tips
Celsius and Fahrenheit are the two most widely used temperature scales in the world. Celsius (°C) is used in almost every country and is the standard in science, medicine, and international contexts. Fahrenheit (°F) is used primarily in the United States for everyday weather and cooking temperatures.
The Conversion Formulas
Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Example: Convert 25°C to Fahrenheit: (25 × 9/5) + 32 = 45 + 32 = 77°F
Example: Convert 98.6°F to Celsius: (98.6 − 32) × 5/9 = 66.6 × 0.556 = 37°C
Quick Mental Math Shortcut
For a fast rough estimate when converting Celsius to Fahrenheit: double the Celsius temperature and add 30. This gives a result within a few degrees for most everyday temperatures. For example, 20°C × 2 = 40 + 30 = 70°F (exact answer is 68°F). For the reverse, subtract 30 and halve: 70°F − 30 = 40 ÷ 2 = 20°C.
Temperature Reference Chart
| Description | Celsius | Fahrenheit |
|---|---|---|
| Absolute zero | -273.15°C | -459.67°F |
| Water freezes | 0°C | 32°F |
| Very cold winter day | -20°C | -4°F |
| Cold day | 0°C | 32°F |
| Cool spring day | 15°C | 59°F |
| Room temperature | 20-22°C | 68-72°F |
| Warm summer day | 30°C | 86°F |
| Hot day | 38°C | 100°F |
| Normal body temp | 37°C | 98.6°F |
| Fever threshold | 38°C | 100.4°F |
| Water boils (sea level) | 100°C | 212°F |
| Baking (moderate oven) | 175°C | 350°F |
| Pizza oven | 260°C | 500°F |
The Third Scale: Kelvin
Scientists use Kelvin (K) rather than Celsius or Fahrenheit. Kelvin starts at absolute zero (the coldest possible temperature) and uses the same size degrees as Celsius. To convert: K = °C + 273.15. Water freezes at 273.15K and boils at 373.15K. There is no "degree" symbol with Kelvin — you write 300 K, not 300°K.
Why Two Different Scales Exist
Fahrenheit was developed by German physicist Daniel Fahrenheit in 1724. He set 0° as the coldest temperature he could achieve in his lab and 96° as human body temperature (later recalibrated to 98.6°F). Celsius was developed by Swedish astronomer Anders Celsius in 1742 using the simpler anchors of water's freezing (0°) and boiling (100°) points. The Celsius scale's simplicity made it the global standard.
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