Convert °F to °C (and back) in real time. Includes Kelvin output, quick presets, color-coded scale, and a full reference chart.
| Description | Fahrenheit (°F) | Celsius (°C) | Kelvin (K) |
|---|---|---|---|
| Absolute zero | −459.67°F | −273.15°C | 0 K |
| −40° crossover | −40°F | −40°C | 233.15 K |
| Extremely cold | −20°F | −28.9°C | 244.26 K |
| Very cold day | 0°F | −17.8°C | 255.37 K |
| Freezing point (water) | 32°F | 0°C | 273.15 K |
| Cool spring day | 50°F | 10°C | 283.15 K |
| Mild weather | 68°F | 20°C | 293.15 K |
| Room temperature | 72°F | 22.2°C | 295.37 K |
| Warm summer day | 86°F | 30°C | 303.15 K |
| Normal body temp | 98.6°F | 37°C | 310.15 K |
| Very hot day | 104°F | 40°C | 313.15 K |
| Boiling point (water) | 212°F | 100°C | 373.15 K |
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Try Brite FreeThe Fahrenheit scale was invented in 1724 by German physicist Daniel Gabriel Fahrenheit. He based his scale on three reference points: the freezing point of a brine solution (0°F), the freezing point of water (32°F), and human body temperature (96°F in his original scale — later refined to 98.6°F). Fahrenheit's thermometers were remarkably accurate for their time, and his scale quickly became adopted across Europe and the British Empire.
The Celsius scale, originally called centigrade, was proposed in 1742 by Swedish astronomer Anders Celsius. His original scale was inverted — 0 meant boiling and 100 meant freezing. After Celsius's death, the scale was reversed to its modern form. The word "Celsius" officially replaced "centigrade" in 1948 when the international scientific community standardized it under the SI unit system.
Today, Celsius is by far the more widely used scale. Only five countries or territories still use Fahrenheit as their primary scale for everyday temperature: the United States, the Bahamas, the Cayman Islands, Liberia, and Palau. The rest of the world — over 190 countries — uses Celsius for weather forecasts, medicine, cooking, and science.
The relationship between Fahrenheit and Celsius is linear but offset. The two scales differ in both their zero points and the size of each degree.
The formula is: °C = (°F − 32) × 5/9
You subtract 32 first because the Fahrenheit zero point is 32 degrees lower than where water freezes. Then you multiply by 5/9 because a Celsius degree is larger — there are 180 Fahrenheit degrees between freezing and boiling, but only 100 Celsius degrees covering the same range. So 100/180 = 5/9.
Example: Convert 77°F to Celsius: (77 − 32) × 5/9 = 45 × 5/9 = 25°C.
The reverse formula is: °F = (°C × 9/5) + 32
Multiply by 9/5 to scale up from Celsius to the wider Fahrenheit range, then add 32 to shift the zero offset.
Example: Convert 20°C to Fahrenheit: (20 × 9/5) + 32 = 36 + 32 = 68°F.
For a rough estimate without a calculator, use the approximation: double the Celsius value and add 30 to get Fahrenheit. Or subtract 30 from Fahrenheit and halve it to get Celsius. This is less accurate but useful for quick conversions — for example, 20°C → (20 × 2) + 30 = 70°F (actual: 68°F).
Kelvin is the SI base unit for temperature, used primarily in science and engineering. Unlike Fahrenheit and Celsius, Kelvin has no negative values — it starts at absolute zero (−273.15°C / −459.67°F), the theoretical lowest possible temperature where molecular motion stops completely.
The formula to convert Celsius to Kelvin is simply: K = °C + 273.15. There are no degree symbols in Kelvin — you write "300 K" not "300°K". The size of one Kelvin increment is identical to one Celsius degree, making conversion straightforward.
Kelvin is used in astrophysics (stellar temperatures reach millions of K), thermodynamics, cryogenics, and color temperature in photography and display technology (a "warm" 3000K bulb vs. a "cool" 6500K daylight LED).
Body temperature is one of the most practical reasons people convert between Fahrenheit and Celsius. American medical packaging, thermometers, and healthcare providers typically use Fahrenheit, while the rest of the world — and most medical literature — uses Celsius.
Normal body temperature is 98.6°F (37°C), though healthy individuals range from about 97°F to 99°F (36.1–37.2°C). Temperature also varies by time of day — typically lowest in the early morning and highest in late afternoon — as well as by age, activity level, and method of measurement.
Fever officially begins at 100.4°F (38°C). A low-grade fever between 99–100.4°F (37.2–38°C) is common with mild infections and may not require medication. Fevers above 103°F (39.4°C) in adults generally warrant medical attention, especially when accompanied by severe headache, stiff neck, or difficulty breathing. A fever above 104°F (40°C) is a medical emergency.
Hypothermia occurs when body temperature drops below 95°F (35°C). Mild hypothermia (89.6–95°F / 32–35°C) causes shivering and confusion; severe hypothermia below 82.4°F (28°C) can be fatal without immediate medical treatment.
Understanding temperature in both scales helps when traveling internationally or following weather news from different countries.
The highest reliably recorded air temperature on Earth is 134°F (56.7°C), measured at Furnace Creek, Death Valley, California, on July 10, 1913. The coldest recorded temperature is −128.6°F (−89.2°C) at Vostok Station, Antarctica, on July 21, 1983.
Cooking is another area where the two scales frequently clash, especially with recipes from different countries. American recipes nearly always use Fahrenheit; British, Australian, and European recipes use Celsius.
When a UK recipe says "180°C fan oven," that is 356°F (approximately 350°F) in a conventional oven — a very common baking temperature for cakes and biscuits.
Beyond everyday use, temperature conversions matter in a wide range of professional fields: