°C = (°F - 32) × 5/9. First subtract 32 from Fahrenheit, then multiply by 5/9 (or 0.5556). For example, 98.6°F: (98.6 - 32) × 5/9 = 66.6 × 0.5556 = 37°C.

32°F = 0°C. This is the freezing point of water — the temperature at which water turns to ice at standard atmospheric pressure.

100°F = 37.78°C. This is close to body temperature (98.6°F/37°C) and considered a hot day or mild fever.

-40° is the same in both scales! -40°F = -40°C. This is the only temperature where the two scales intersect.

Normal body temperature is 37°C (98.6°F). A fever is typically considered 38°C (100.4°F) or higher.

Fahrenheit was adopted in the US before the metric system became standard. While most countries switched to Celsius, the US retained Fahrenheit for everyday use, though scientific contexts use Celsius/Kelvin.

Water boils at 212°F = 100°C at standard atmospheric pressure (sea level). At higher altitudes, water boils at lower temperatures.

0°F = -17.78°C. Zero Fahrenheit was originally set as the coldest temperature Daniel Fahrenheit could create in his lab using a salt-ice mixture.

Quick trick: Subtract 30, then divide by 2. For 70°F: (70-30)/2 = 20°C. It's not exact (actual: 21.1°C) but close enough for everyday use.

Room temperature is typically 68-72°F (20-22°C). Most indoor thermostats are set in this range for comfort.