Which Is Colder: Minus 40°C or Minus 40°F? A Complete Guide to Understanding Temperature Conversions

At first glance, the question seems simple, but it opens a fascinating window into how we measure temperature, why different parts of the world use different systems, and how these systems relate at extreme temperatures.

The answer may surprise you:

Minus 40°C is exactly equal to minus 40°F.
That’s right — it’s the one point where the two temperature scales meet.

Let’s unpack why this happens and what else you should know about Celsius vs Fahrenheit.

Celsius vs Fahrenheit: What’s the Difference?

What Is the Celsius Scale?

• Origin: Developed in 1742 by Swedish astronomer Anders Celsius.
• Definition: 0°C is the freezing point of water, 100°C is the boiling point (at sea level).
• Used In: Most of the world — Europe, Asia, Africa, Australia, and nearly all scientific work.
• Conversion Formula:
  °F = (°C × 9/5) + 32

What Is the Fahrenheit Scale?

• Origin: Created in 1724 by German physicist Daniel Gabriel Fahrenheit.
• Definition: 32°F is the freezing point of water, and 212°F is the boiling point.
• Used In: Primarily the United States, some Caribbean nations, and their territories.
• Conversion Formula:
  °C = (°F − 32) × 5/9

So, Which Is Colder: -40°C or -40°F?

They are the same temperature.
This is a unique point on the scale where:

-40°C × 9/5 + 32 = -40°F

It's the only temperature where Celsius and Fahrenheit readings match.

Why Does This Confuse People?

It’s mainly because:

• Fahrenheit numbers are larger for typical room and outdoor temperatures (e.g., 70°F ≈, 21°C), which makes people assume a direct scale-up.
• Most people never encounter extreme cold, so they don’t often see the overlap point.
• In educational systems where only one scale is taught, there’s little intuitive comparison.

Why Are There Two Temperature Scales?

1. Historical Context
   1. Fahrenheit was created for practical use with mercury thermometers and was easier to divide using the tools of the time.
   2. Celsius was aligned to the water-based metric system, which later became globalized.
2. Cultural Adoption
   1. The metric system (Celsius) became globally accepted due to its ease of use and scientific accuracy.
   2. The imperial system (Fahrenheit) persisted in the US due to historical inertia and public familiarity.

Real-World Reference Points

Where on Earth Has It Hit -40?

Places like Siberia, northern Canada, Greenland, and parts of Scandinavia regularly dip to -40 or lower in winter. For instance:

• Sweden recorded -43°C in February 2021 
• Yukon, Canada, and Siberia also routinely experience these levels.

In such areas, both Celsius and Fahrenheit users shiver equally — literally!

Quick Celsius to Fahrenheit Reference

This table helps you visualize how the two scales behave across freezing temperatures.

How Cold Feels at -40

Whether it’s -40°C or -40°F, the result is the same:

• Metal sticks to skin.
• Vehicles may not start.
• Skin freezes in minutes without protection.
• Wind chill makes it even worse.

At this temperature, your eyelashes may freeze, and it’s considered dangerously cold regardless of the scale.

Which Countries Use Which?

Why Don’t We Just Use One System?

• Cultural and infrastructural momentum is hard to overcome.
• Temperature scales are embedded into weather reporting, oven dials, car thermostats, etc.
• It would require massive systemic changes, especially in countries like the U.S.

That said, many scientific fields and global collaborations are metric-first, including weather models, space exploration, and climate science.

Celsius or Fahrenheit: Which Is Colder at -40?

Both are the same. This is the only point where the two scales align.