A temperature converter is a free online tool that instantly converts any temperature value between the three major temperature scales — Celsius, Fahrenheit, and Kelvin — with complete accuracy and no manual calculation required. Enter a temperature in any scale and see the precise equivalent in both other scales simultaneously, updated in real time as you type.
Celsius — also called centigrade — is the temperature scale used in everyday life by the vast majority of the world. Developed by Swedish astronomer Anders Celsius in 1742, it defines:
Normal human body temperature: 37.0°C | Room temperature: typically 20–22°C
Fahrenheit is the temperature scale used for everyday measurement in the United States. Developed by German physicist Daniel Gabriel Fahrenheit in 1724, it defines:
A Fahrenheit degree is 5/9 the size of a Celsius degree — smaller than a Celsius degree.
Kelvin is the absolute temperature scale used universally in science, engineering, and technology. It is the SI base unit of thermodynamic temperature. Key characteristics:
| Convert | Formula | Example |
|---|---|---|
| Celsius → Fahrenheit | °F = (°C × 9/5) + 32 | 25°C → (25 × 1.8) + 32 = 77°F |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 | 98.6°F → (98.6 − 32) ÷ 1.8 = 37°C |
| Celsius → Kelvin | K = °C + 273.15 | 100°C → 100 + 273.15 = 373.15 K |
| Kelvin → Celsius | °C = K − 273.15 | 0 K → 0 − 273.15 = −273.15°C |
| Fahrenheit → Kelvin | K = (°F − 32) × 5/9 + 273.15 | 32°F → 0 + 273.15 = 273.15 K |
| Kelvin → Fahrenheit | °F = (K − 273.15) × 9/5 + 32 | 373.15 K → 100 × 1.8 + 32 = 212°F |
| Description | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | −273.15°C | −459.67°F | 0 K |
| Liquid nitrogen | −196°C | −320.8°F | 77.15 K |
| Scales intersect | −40°C | −40°F | 233.15 K |
| Water freezing | 0°C | 32°F | 273.15 K |
| Room temperature | 20–22°C | 68–72°F | 293–295 K |
| Human body (normal) | 37°C | 98.6°F | 310.15 K |
| Low-grade fever | 38°C | 100.4°F | 311.15 K |
| High fever | 40°C | 104°F | 313.15 K |
| Water boiling | 100°C | 212°F | 373.15 K |
| Description | Celsius | Fahrenheit | Gas Mark (UK) |
|---|---|---|---|
| Very cool | 120°C | 250°F | ½ |
| Cool | 140°C | 275°F | 1 |
| Moderate | 180°C | 350°F | 4 |
| Moderately hot | 190°C | 375°F | 5 |
| Hot | 200°C | 400°F | 6 |
| Very hot | 220°C | 425°F | 7 |
| Extremely hot | 230°C | 450°F | 8 |
Unlike length or weight conversions — which involve only multiplication — temperature conversion requires both multiplication and addition or subtraction, because the three scales have different zero points as well as different degree sizes. This two-step requirement makes mental temperature conversion significantly more error-prone:
Converting 20°C to Fahrenheit: multiply by 1.8 AND add 32. Most people remember one operation or the other — applying only multiplication gives 36°F (wrong) instead of 68°F (correct). Both steps are required, in the correct order.
💡 The −40° Curiosity: The only temperature where Celsius and Fahrenheit give identical readings is −40°. Working out the algebra: setting °F = °C: x = (x × 1.8) + 32 → −0.8x = 32 → x = −40. This is the only intersection point of the two scales — approximately the temperature of the most extreme winter conditions in Siberia, Canada, and Alaska.
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Multiply by 9/5 (or 1.8) and then add 32: °F = (°C × 1.8) + 32. For example, 100°C = (100 × 1.8) + 32 = 180 + 32 = 212°F.
Subtract 32, then multiply by 5/9 (or divide by 1.8): °C = (°F − 32) × 5/9. The subtraction MUST happen before the multiplication — reversing the order gives a wrong result.
37°C = (37 × 1.8) + 32 = 66.6 + 32 = 98.6°F. This is normal human body temperature — one of the most commonly needed temperature conversions in medical and health contexts.
The two scales give identical numerical readings at exactly −40°. Both −40°C and −40°F represent the same temperature — this is the only point where the Celsius and Fahrenheit scales intersect.
The degree symbol (°) is not used with Kelvin because the Kelvin is an absolute scale with a natural zero point — not a relative scale like Celsius and Fahrenheit. You write 300 K, not 300°K. The 2019 SI redefinition formalised this convention.
Subtract 32, then multiply by 5/9. A 350°F oven = (350 − 32) × 5/9 = 318 × 0.5556 = 176.7°C — typically rounded to 175°C or 180°C in practice.
The United States is the primary country using Fahrenheit for everyday temperature measurement. A small number of other territories including the Bahamas, Belize, and the Cayman Islands also use Fahrenheit. Every other country in the world uses Celsius for everyday temperature, with Kelvin used universally in science and engineering.
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