🔄 Converters
🌡️ 🌡️ Temperature Converter: Celsius, Fahrenheit, and Kelvin
Learn how to convert temperatures between Celsius, Fahrenheit, and Kelvin. Covers the exact formulas, quick mental shortcuts, absolute zero, and key reference temperatures.
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Temperature is one of the most frequently converted measurements — reading international recipes, following foreign weather forecasts, or working with scientific literature that uses Kelvin. Three scales dominate: Celsius (most of the world), Fahrenheit (United States), and Kelvin (science).
The Three Scales
- Celsius (°C): 0°C = water freezes, 100°C = water boils. Used by nearly every country for weather and cooking.
- Fahrenheit (°F): Developed by Fahrenheit in 1724. Used primarily in the US for everyday temperatures.
- Kelvin (K): SI base unit. Absolute zero (0 K) is the lowest theoretically possible temperature. No degree symbol — written "300 K." Used universally in science.
Conversion Formulas
| Convert |
Formula |
| °C → °F | °F = (°C × 9/5) + 32 |
| °F → °C | °C = (°F − 32) × 5/9 |
| °C → K | K = °C + 273.15 |
| K → °C | °C = K − 273.15 |
| °F → K | K = (°F − 32) × 5/9 + 273.15 |
Worked Examples
- Body temp 37°C → °F: (37 × 9/5) + 32 = 66.6 + 32 = 98.6°F
- Oven 350°F → °C: (350 − 32) × 5/9 = 318 × 5/9 = 176.7°C
- Liquid nitrogen −196°C → K: −196 + 273.15 = 77.15 K
Quick Mental Approximations
- °C → °F: Double the Celsius, add 30. (20°C → 70°F; actual 68°F — good enough for weather)
- °F → °C: Subtract 30, halve. (70°F → 20°C; actual 21.1°C)
Key Reference Temperatures
| Reference |
°C |
°F |
K |
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20–22 | 68–72 | 293–295 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
❓ Frequently Asked Questions
How do I convert Celsius to Fahrenheit?▼
°F = (°C × 9/5) + 32. For 25°C: (25 × 1.8) + 32 = 77°F. Quick approximation: double Celsius and add 30 (accurate to within 2–3°F for common temperatures).
How do I convert Fahrenheit to Celsius?▼
°C = (°F − 32) × 5/9. For 98.6°F: (98.6 − 32) × 5/9 = 37°C. Quick approximation: subtract 30 and halve (70°F → 20°C).
What is absolute zero?▼
Absolute zero is 0 K = −273.15°C = −459.67°F — the theoretical lowest possible temperature where all atomic motion ceases. It has never been achieved; the coldest laboratory temperatures reach within billionths of a degree above it.
Why does the US use Fahrenheit?▼
The US adopted Fahrenheit before the metric system existed. When most countries switched to metric Celsius in the 20th century, the US maintained Fahrenheit for everyday use due to cultural inertia. The US uses Celsius in science, medicine, and international contexts.
At what temperature are Celsius and Fahrenheit equal?▼
At −40°: −40°C = −40°F exactly. Verify: (−40 × 9/5) + 32 = −72 + 32 = −40°F. Below −40°, Fahrenheit readings are numerically lower; above −40°, Fahrenheit readings are higher.