Temperature
Celsius vs Fahrenheit
Two scales, one world. Here's how they relate — and how to convert instantly.
Celsius
Water freezes at 0°, boils at 100°
Fahrenheit
Water freezes at 32°, boils at 212°
At a glance
| Celsius | Fahrenheit | |
|---|---|---|
| Water freezes | 0 °C | 32 °F |
| Water boils | 100 °C | 212 °F |
| Human body temp | 37 °C | 98.6 °F |
| Comfortable room temp | 20–22 °C | 68–72 °F |
| Moderate oven | 180 °C | 356 °F |
| Absolute zero | −273.15 °C | −459.67 °F |
Pick Celsius
Science, most of the world, international recipes, and weather reporting in every country except the United States, Bahamas, Belize, Cayman Islands, and Palau.
Pick Fahrenheit
Everyday US weather, US oven temperatures, US recipes, and any context where you are communicating with an American audience.
The conversion formulas
Converting between the two scales requires two steps: a scale change and an offset.
Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Example: Convert 25°C (a warm spring day) to Fahrenheit. - 25 × 9/5 = 25 × 1.8 = 45 - 45 + 32 = 77°F ✓
Example: Convert 98.6°F (normal body temperature) to Celsius. - 98.6 − 32 = 66.6 - 66.6 × 5/9 = 66.6 × 0.5556 = 37°C ✓
The formula looks simple but is easy to get backwards. The 9/5 factor (1.8) is the ratio of the two scales' degree sizes. A 1°C change equals a 1.8°F change. The +32 and −32 offsets account for the different zero points.
Mental math shortcuts
The exact formula is cumbersome for mental math. These shortcuts get you close enough for everyday use:
Quick Celsius → Fahrenheit estimate: Double the Celsius temperature, then add 30. - 20°C → 20 × 2 + 30 = 70°F (actual: 68°F — close enough) - 30°C → 30 × 2 + 30 = 90°F (actual: 86°F — within 5%)
Quick Fahrenheit → Celsius estimate: Subtract 30, then halve. - 80°F → (80 − 30) ÷ 2 = 25°C (actual: 26.7°C — close) - 60°F → (60 − 30) ÷ 2 = 15°C (actual: 15.6°C — very close)
The doubling/halving method trades precision for speed. For casual weather comparisons, it is perfectly adequate. For oven temperatures or scientific work, use the exact formula.
The one exact crossover point: −40° is the same in both scales (−40°C = −40°F). This is a useful sanity check for mental math.
Key reference points to memorize
Rather than converting every time, memorize a handful of anchor points:
0°C / 32°F — Water freezes. Below this, ice and snow. 10°C / 50°F — Cool but not cold. A light jacket weather. 20°C / 68°F — Comfortable indoor room temperature. 30°C / 86°F — Hot summer day. Above this, uncomfortable without AC. 37°C / 98.6°F — Normal human body temperature. 100°C / 212°F — Water boils at sea level. 180°C / 356°F — Moderate baking oven (often written as 350°F in US recipes). 200°C / 392°F — Hot oven, roasting temperature.
With these anchors, you can interpolate any temperature without needing the formula. If someone says it is 25°C outside, you know that is between 20°C (68°F) and 30°C (86°F), so roughly 77°F — a warm, pleasant day.