The Two Scales
Celsius (°C) is the metric standard. Water freezes at 0°C and boils at 100°C. Used in most of the world.
Fahrenheit (°F) is used primarily in the United States. Water freezes at 32°F and boils at 212°F.
The scales overlap at one exact point: −40° is identical in both systems.
0°C = 32°F
Water freezes (°C)
100°C = 212°F
Water boils (°C)
37°C = 98.6°F
Body temperature
−40°C = −40°F
Equal point
Celsius → Fahrenheit Formula
°F = (°C × 9/5) + 32
Or written differently: °F = (°C × 1.8) + 32
Example 1: Body temperature
Normal body temperature is 37°C. What is it in Fahrenheit?
°F = (37 × 1.8) + 32
°F = 66.6 + 32
°F = 98.6°F ✓
Example 2: A hot summer day
35°C in Fahrenheit:
°F = (35 × 1.8) + 32
°F = 63 + 32
°F = 95°F
Fahrenheit → Celsius Formula
°C = (°F − 32) × 5/9
Or: °C = (°F − 32) ÷ 1.8
Example: Oven temperature
A recipe calls for 350°F. What is that in Celsius?
°C = (350 − 32) ÷ 1.8
°C = 318 ÷ 1.8
°C = 176.7°C (round to 175°C or 180°C for a home oven)
°F = (°C × 1.8) + 32
Examples:
37°C → (37 × 1.8) + 32 = 98.6°F (body temp)
35°C → (35 × 1.8) + 32 = 95°F (hot day)
0°C → (0 × 1.8) + 32 = 32°F (freezing)Mental-Math Shortcut
For a fast estimate without a calculator:
°C → °F: Double the Celsius, then add 30
| Actual °C | Shortcut (×2+30) | Exact °F | Error |
|---|---|---|---|
| 0°C | 0 + 30 = 30 | 32°F | −2 |
| 10°C | 20 + 30 = 50 | 50°F | 0 ✓ |
| 20°C | 40 + 30 = 70 | 68°F | +2 |
| 30°C | 60 + 30 = 90 | 86°F | +4 |
| 40°C | 80 + 30 = 110 | 104°F | +6 |
The shortcut is accurate to within ±5°F for everyday temperatures. It breaks down at extremes.
Reference Table: Common Temperatures
| Description | °C | °F |
|---|---|---|
| Absolute zero | −273.15 | −459.67 |
| Water freezes | 0 | 32 |
| Cold winter day | −10 | 14 |
| Comfortable room | 22 | 71.6 |
| Body temperature | 37 | 98.6 |
| Hot summer day | 40 | 104 |
| Water boils | 100 | 212 |
| Oven (medium) | 180 | 356 |
| Oven (high) | 220 | 428 |
Why Two Scales Exist
Daniel Gabriel Fahrenheit (1686–1736) proposed his scale using a saltwater brine mixture as 0° and human body temperature as ~96°. The scale was later adjusted and standardized.
Anders Celsius (1701–1744) proposed a scale with 0° at boiling and 100° at freezing — the opposite of today’s convention. It was later reversed after his death.
The scientific community adopted Celsius as part of the metric (SI) system. The US retained Fahrenheit largely due to historical inertia and the cost of switching.
- 1724
Daniel Gabriel Fahrenheit proposes his temperature scale
Used saltwater brine as 0° and human body temperature as ~96°. Later standardized.
- 1742
Anders Celsius proposes centigrade scale
Originally with 0° at boiling and 100° at freezing — the reverse of today. Inverted after his death.
- 1960
Celsius adopted as the SI standard worldwide
The scientific community standardizes on Celsius. US retains Fahrenheit due to historical inertia.
Use our Temperature Converter to instantly convert between Celsius, Fahrenheit, and Kelvin for any value.