Celsius, Fahrenheit, and Kelvin: Key Reference Points
Three main temperature scales are in everyday and scientific use. Celsius (°C) is the global standard, with water freezing at 0°C and boiling at 100°C at sea level. Fahrenheit (°F) is used in the US, where water freezes at 32°F and boils at 212°F. Kelvin (K) is the scientific absolute scale starting at absolute zero (-273.15°C), with no negative values.
Essential Reference Temperatures
-40°C = -40°F (the only temperature where the scales are equal) / 0°C = 32°F / 20°C = 68°F (comfortable room temperature) / 37°C = 98.6°F (normal body temperature) / 100°C = 212°F (water boiling point at sea level). For oven temperatures: 350°F = 176.7°C, 400°F = 204.4°C, 450°F = 232.2°C.
Quick Mental Conversion Tips
°C to °F: multiply by 2 and add 30 (accurate to ±2°F for typical weather temperatures). Example: 25°C → 50+30=80°F (actual: 77°F). °F to °C: subtract 30 and divide by 2. Example: 86°F → (86-30)/2=28°C (actual: 30°C). For precision, use the calculator above.
When Kelvin and Rankine Are Used
Kelvin is used in thermodynamics, chemistry, astronomy, and physics. The surface of the Sun is about 5,778 K (5,505°C). The cosmic microwave background is 2.725 K. Rankine (°R) is the imperial absolute scale used in some US engineering fields. 1°R = 5/9 K; absolute zero is 0°R = 0 K.
Frequently Asked Questions
98.6°F = (98.6 - 32) × 5/9 = 37°C — normal human body temperature. A fever is typically considered 100.4°F (38°C) or above.
350°F = (350 - 32) × 5/9 = 176.7°C. This is a common "moderate oven" temperature for baking cakes and cookies.