-40 degrees Celsius is equal to -40 degrees Fahrenheit.
The Only Temperature Where Celsius Equals Fahrenheit
There's exactly one temperature where you don't need to convert between Celsius and Fahrenheit: minus 40 degrees. At this frigid point, both thermometers show the same number.
This isn't a coincidence or a rounding trick. It's the mathematical consequence of how these two temperature scales were designed.
The Math Behind the Magic
The standard conversion formula is F = (C × 9/5) + 32. When you plug in -40 for C, you get:
- F = (-40 × 9/5) + 32
- F = -72 + 32
- F = -40
Working backwards from Fahrenheit to Celsius using C = (F - 32) × 5/9 produces the same result. It's the only temperature where this happens.
Why Just This One Point?
The Celsius and Fahrenheit scales have different zero points and different degrees of separation. Celsius sets 0° at water's freezing point and 100° at boiling. Fahrenheit uses 32° for freezing and 212° for boiling.
These scales are like two lines on a graph that cross at exactly one point: -40. Above that temperature, Fahrenheit numbers are always higher. Below it, Celsius numbers become more negative faster.
Fun perspective: This crossover happens at a temperature cold enough to freeze your exposed skin in minutes. In most of Canada, Russia, and Antarctica, -40° weather occasionally occurs—and at that moment, the temperature debate between Celsius and Fahrenheit fans becomes wonderfully moot.
Other Temperature Curiosities
While -40 is the only intersection for Celsius and Fahrenheit, there are other temperature quirks:
- Kelvin and Celsius differ by a constant 273.15 degrees, so they never intersect
- Rankine and Fahrenheit also run parallel, offset by 459.67 degrees
- On the Celsius scale, body temperature (37°C) nearly doubles to 98.6°F
The -40 convergence remains unique because it's the only whole number where two major temperature scales align perfectly—a mathematical curiosity with real-world implications for anyone experiencing extreme cold.