Temperature Conversion: Celsius, Fahrenheit, and Kelvin

An American recipe calls for 350°F, but your oven reads Celsius. A European news report says 25°C, and you want to know if you need a jacket. Temperature conversion is one of the most common everyday math problems — and one of the easiest to get wrong without the formulas.

The Three Scales

• Celsius (°C): Used worldwide for everyday temperatures. Water freezes at 0°C and boils at 100°C.
• Fahrenheit (°F): Used mainly in the United States. Water freezes at 32°F and boils at 212°F.
• Kelvin (K): The scientific scale. 0 K is absolute zero; Kelvin has no negative values and uses the same step size as Celsius.

The Exact Formulas

C to F:  F = C × 9/5 + 32
F to C:  C = (F - 32) × 5/9
C to K:  K = C + 273.15
K to C:  C = K - 273.15

Worked examples:

100°C × 9/5 + 32 = 212°F
(68°F - 32) × 5/9 = 20°C
25°C + 273.15 = 298.15 K

Mental Shortcuts for Everyday Life

When you just need a close answer, these approximations cover most situations:

• Double the Celsius and add 30 for Fahrenheit (close between 0°C and 30°C).
• Subtract 30 and halve the Fahrenheit for Celsius.
• 0°C is 32°F, 10°C is 50°F, 20°C is 68°F, 30°C is 86°F, and 37°C is roughly body temperature (98.6°F).

When Precision Matters

Recipes, laboratory work, and HVAC settings need exact values, not approximations. Ovens hold narrow temperature tolerances, and scientific constants depend on Kelvin. When precision matters, reach for a converter instead of doing long division in your head.