Temperature conversion is one of the most searched calculations online — travellers, cooks, scientists, and medical professionals all need it. Here's everything you need: the exact formulas, a reference chart, and mental shortcuts that work without a calculator.
The Formulas
Celsius to Fahrenheit
°F = (°C × (9) / (5)) + 32
Or equivalently: °F = (°C × 1.8) + 32
Fahrenheit to Celsius
°C = (°F - 32) × (5) / (9)
Or equivalently: °C = (°F − 32) ÷ 1.8
Celsius to Kelvin
K = °C + 273.15
Fahrenheit to Kelvin
K = (°F - 32) × (5) / (9) + 273.15
Worked Examples
Convert 100°C to Fahrenheit (boiling point of water):
°F = (100 × 1.8) + 32 = 180 + 32 = 212°F
Convert 98.6°F to Celsius (normal body temperature):
°C = (98.6 - 32) ÷ 1.8 = 66.6 ÷ 1.8 = 37°C
Convert 0°C to Fahrenheit (freezing point of water):
°F = (0 × 1.8) + 32 = 0 + 32 = 32°F
Convert 72°F to Celsius (comfortable room temperature):
°C = (72 - 32) ÷ 1.8 = 40 ÷ 1.8 = 22.2°C
Quick Reference Chart
| Celsius | Fahrenheit | Context |
|---|---|---|
| −40°C | −40°F | The only temperature equal on both scales |
| −18°C | 0°F | US Fahrenheit zero — freezer temperature |
| 0°C | 32°F | Water freezes |
| 10°C | 50°F | Cold autumn day |
| 16°C | 61°F | Cool but comfortable |
| 20°C | 68°F | Room temperature (cool) |
| 22°C | 72°F | Room temperature (comfortable) |
| 25°C | 77°F | Warm room / mild summer day |
| 30°C | 86°F | Hot summer day |
| 37°C | 98.6°F | Normal human body temperature |
| 40°C | 104°F | Fever / very hot day |
| 100°C | 212°F | Water boils (at sea level) |
| 180°C | 356°F | Moderate oven |
| 220°C | 428°F | Hot oven |
Mental Shortcuts (No Calculator)
The exact formula requires multiplication and addition in a specific order. These shortcuts sacrifice a little precision for speed.
Quick C → F estimate:
- Double the Celsius temperature
- Subtract 10%
- Add 32
Example: 25°C → 25×2 = 50 → 50 − 5 = 45 → 45 + 32 = 77°F ✓ (exact)
Quick F → C estimate:
- Subtract 32
- Divide by 2
- Add 10%
Example: 77°F → 77 − 32 = 45 → 45 ÷ 2 = 22.5 → 22.5 + 2.25 = ~24.75°C (exact is 25°C — close enough)
Even quicker (rougher): To convert Celsius to Fahrenheit in your head, double it and add 30. To go back, subtract 30 and halve. Error of about 2–4°F but fine for weather conversations.
Why Two Scales Exist
Fahrenheit was developed in 1724 by Daniel Gabriel Fahrenheit. He based it on three reference points: the freezing point of a brine solution (0°F), the freezing point of water (32°F), and human body temperature (originally set at 96°F, later adjusted to 98.6°F). The scale is still used in the United States and a few other countries.
Celsius (originally Centigrade) was developed in 1742 by Anders Celsius. It places 0° at water's freezing point and 100° at water's boiling point — making it logical for scientific use. Almost every country in the world uses Celsius for everyday temperature.
Kelvin is the SI unit of temperature used in science. It starts at absolute zero (−273.15°C), the theoretical point where all molecular motion stops. There are no negative Kelvin values.
Cooking Temperatures
Ovens are often set in Fahrenheit in older recipes but Celsius in modern ones. Key conversions:
| Use | Fahrenheit | Celsius | Gas Mark |
|---|---|---|---|
| Slow cook | 300°F | 150°C | 2 |
| Moderate oven | 350°F | 180°C | 4 |
| Moderately hot | 375°F | 190°C | 5 |
| Hot oven | 400°F | 200°C | 6 |
| Very hot | 425°F | 220°C | 7 |
| Extremely hot | 450°F | 230°C | 8 |
Convert Temperature Now
Our temperature converter handles Celsius, Fahrenheit, and Kelvin — enter any value and instantly see all three.