Temperature Converter
Convert between Fahrenheit, Celsius, and Kelvin with instant results and formulas shown. Includes reference points table and the −40 crossover explained.
Formulas, assumptions, and rounding are documented in our calculator methodology.
Enter a temperature in any field — all other scales update instantly.
Key Reference Points
Formulas: °C to °F = (°C × 9/5) + 32 · °C to K = °C + 273.15
Temperature Conversion Formulas
Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Fahrenheit: °F = (°C × 9/5) + 32. Celsius to Kelvin: K = °C + 273.15. Kelvin to Celsius: °C = K − 273.15. Fahrenheit to Kelvin: K = (°F − 32) × 5/9 + 273.15. Quick shortcut for °F to °C: subtract 32, then halve (gives an approximation within ~1–2°C for everyday temperatures).
Temperature Reference Points
Absolute zero: −459.67°F / −273.15°C / 0 K. Dry ice sublimes: −109.3°F / −78.5°C. Water freezes: 32°F / 0°C. Cold room: 50°F / 10°C. Comfortable room: 68–72°F / 20–22°C. Body temperature: 98.6°F / 37°C. Water boils (sea level): 212°F / 100°C. Standard baking: 350°F / 177°C. Self-cleaning oven: 900°F / 482°C.
The −40 Crossover: Where Fahrenheit Equals Celsius
At exactly −40 degrees, the Fahrenheit and Celsius scales read the same number. This is because their zero points are offset (Celsius is defined by water's freezing/boiling points; Fahrenheit's zero was originally based on a stable salt-ice mixture), but they cross when you work the algebra: (°F − 32) × 5/9 = °F. Solving gives °F = −40. This crossover is occasionally useful as a mental check: if a temperature is given as −40, it is the same in both scales.
Why Do Some Countries Use Fahrenheit and Others Celsius?
The Fahrenheit scale was proposed by Daniel Fahrenheit in 1724; it was the dominant scale in English-speaking countries for centuries. In 1742, Anders Celsius proposed his centigrade (now Celsius) scale. Most of the world adopted Celsius as part of the metric system in the 20th century. The United States retained Fahrenheit for everyday use (though US science uses Celsius and Kelvin). When following international recipes, weather, or medical guidance, check which scale is being used.
Frequently Asked Questions
- Subtract 32, then multiply by 5/9. Formula: °C = (°F − 32) × 5/9. Examples: 32°F = 0°C (freezing). 98.6°F = 37°C (body temp). 212°F = 100°C (boiling). 350°F ≈ 177°C (baking).
- Multiply by 9/5, then add 32. Formula: °F = (°C × 9/5) + 32. Examples: 0°C = 32°F. 20°C = 68°F (cool room). 37°C = 98.6°F. 100°C = 212°F.
- Both scales read the same value at exactly −40 degrees: −40°F = −40°C. This happens because the scales have different zero points (Celsius: water freezing; Fahrenheit: a brine solution) but converge at this negative value. The math: (−40 − 32) × 5/9 = −72 × 5/9 = −40.
- Absolute zero (0 K) is the coldest possible temperature — the point at which particles have no thermal energy. In Fahrenheit: −459.67°F. In Celsius: −273.15°C. In practice, temperatures within a few billionths of a degree above absolute zero have been achieved in laboratory settings.
- The commonly cited normal body temperature is 37°C (98.6°F), but normal varies by individual, time of day, and measurement method. A more accurate range is 36.1–37.2°C (97–99°F). A temperature above 38°C (100.4°F) is generally considered a fever.