Celsius to Fahrenheit

The exact formula is: °F = (°C × 9/5) + 32. This can also be written as °F = (°C × 1.8) + 32. To apply it: multiply the Celsius value by 9, divide by 5, then add 32. Example: 25°C → (25 × 9 / 5) + 32 = 45 + 32 = 77°F. The formula comes from the fact that there are 180 Fahrenheit degrees between freezing (32°F) and boiling (212°F), while there are 100 Celsius degrees over the same range — a ratio of 180/100 = 9/5 = 1.8.

100°C = 212°F. This is the boiling point of water at sea level (standard atmospheric pressure of 1 atm / 101.325 kPa). The calculation: (100 × 9/5) + 32 = 180 + 32 = 212°F. At higher altitudes, water boils at lower temperatures — for example, at 3,000 meters (9,843 feet), water boils at approximately 90°C = 194°F due to reduced atmospheric pressure.

37°C = 98.6°F. This is the commonly cited 'normal' human body temperature. However, more recent research (Stanford University, 2020) suggests the average modern adult body temperature is closer to 36.6°C (97.9°F), with 37°C being slightly above average. Normal body temperature ranges from 36.1°C to 37.2°C (97°F to 99°F) and varies by time of day, measurement location, age, and individual.

Fahrenheit is used primarily in the United States, its territories, and the Cayman Islands. All other countries — including Canada (officially), the United Kingdom (informally), and virtually all of Asia, Europe, Africa, and South America — use Celsius. The scientific community worldwide uses Celsius (and Kelvin for absolute temperatures). The US is one of only three countries that has not officially adopted the metric system, alongside Myanmar and Liberia.

A fast mental approximation: double the Celsius temperature and add 30. This gives a result within 2–4°F for the range of everyday temperatures. Examples: 0°C → 0×2+30 = 30°F (actual: 32°F). 20°C → 20×2+30 = 70°F (actual: 68°F). 30°C → 30×2+30 = 90°F (actual: 86°F). For more accuracy, use the rule: multiply by 2, subtract 10%, add 32. Example: 20°C → 40 − 4 + 32 = 68°F (exact).