Celsius and Centigrade: What Most People Get Wrong About the Difference

You’re standing in a lab or maybe just staring at a weather app, and you see that little "C" symbol. You call it Celsius. Your grandmother might call it Centigrade. Are you both talking about the same thing? Basically, yes. But if you’re a stickler for scientific history or precise metrology, there is a massive story behind why we stopped using one name and started using the other. It isn't just a synonym swap. It was a global rebranding effort that took place in 1948 to fix a naming conflict that almost nobody remembers today.

What is the difference between Celsius and Centigrade?

The short answer is that there is no difference in the actual temperature value. If it's $25^{\circ}C$ outside, it is 25 degrees Celsius and 25 degrees Centigrade. They are identical in magnitude. However, the term "Centigrade" is technically obsolete. It’s like calling a "refrigerator" an "icebox." People know what you mean, but in the world of professional science and international standards, "Celsius" is the only correct term.

The word "Centigrade" comes from the Latin centum (one hundred) and gradus (steps or degrees). It literally means "divided into 100 degrees." This made perfect sense because the scale was built on the idea that water freezes at 0 and boils at 100. It’s a base-100 system. Simple. Elegant. But there was a problem brewing in the international community.

The 1948 Name Change

In 1948, the 9th General Conference on Weights and Measures (CGPM) met to tidy up scientific terminology. They had a specific reason for killing off the word Centigrade. In several languages—particularly French and Spanish—the term "centigrade" was already being used to describe an angular measurement. Specifically, it was one-hundredth of a "grade" (a unit of angular measure where a right angle is 100 grades).

Imagine being a French physicist in the 1940s. You’re trying to calculate the thermal expansion of a metal rod at a certain angle. You say "centigrade," and suddenly nobody knows if you're talking about how hot the rod is or the angle at which it's leaning. It was a linguistic nightmare for precision.

To fix this, the CGPM decided to name the scale after the man who (sort of) invented it: Anders Celsius.

Who was Anders Celsius?

Anders Celsius was an 18th-century Swedish astronomer. He was a brilliant guy, but he had a weird idea. When he first proposed his scale in 1742, he actually put 0 degrees at the boiling point of water and 100 degrees at the freezing point.

Yes, you read that right. In the original Celsius scale, a higher number meant it was colder.

It was upside down. If you were sick with a fever, your temperature would go down. It stayed that way until after his death in 1744, when other scientists—most notably Carl Linnaeus, the famous botanist—flipped the scale to the orientation we use today. We kept the name, but we fixed the direction.

💡 You might also like: 8 to the Power of 2: Why This Simple Math Fact Actually Matters

The Technical Precision of the Modern Scale

While we often say Celsius is based on water, that’s not strictly true anymore. Since 1954, the scale has been defined by Absolute Zero and the triple point of VSMOW (Vienna Standard Mean Ocean Water).

The triple point is that magical state where water exists as a solid, liquid, and gas simultaneously. It is defined as exactly $0.01^{\circ}C$. This shift moved the scale away from "Centigrade" logic (the 100-step water scale) and into the realm of thermodynamic temperature.

Later, in 2019, the definition changed again. The International System of Units (SI) now defines the Celsius scale based on the Boltzmann constant. This means the degree Celsius is now linked to the average kinetic energy of particles rather than just the behavior of a specific pot of water in a lab.

Why "Centigrade" Lingers in Our Vocabulary

Language is stubborn. We still say "taping a show" even though we use digital DVRs. We still "dial" a phone even though there's no rotary wheel. "Centigrade" persists because it’s descriptive. It tells you exactly what the scale is: a hundred steps.

💡 You might also like: MH-60 Jayhawk: Why the Coast Guard is Betting Everything on This One Helicopter

In the UK, the transition took a long time. The BBC didn't fully switch to saying "Celsius" in weather reports until the mid-1980s. Even today, you’ll find older textbooks or legacy engineering documents that use the old term. If you’re writing a scientific paper today, though, using "Centigrade" is a fast way to get a "please revise" note from your editor.

Common Misconceptions

People often think Celsius is the "Metric" version of Fahrenheit. While Celsius is the standard for the Metric system (SI), Fahrenheit was actually the first "scientific" scale to gain wide adoption because it offered more precision without using decimals.

Another misconception is that 0 Celsius is "no heat." Nope. 0 Celsius is just where water turns to ice. True "no heat" is Absolute Zero, which is $-273.15^{\circ}C$. If you're doing serious chemistry or physics, you’re likely using Kelvin anyway.

The relationship between Kelvin and Celsius is simple:
$K = {^{\circ}C} + 273.15$

The size of the "degree" is exactly the same in both Kelvin and Celsius. Only the starting point changes.

Real-World Implications of the Name

Does it matter what you call it? For your oven or your thermostat, not really. But in global trade and manufacturing, the distinction is vital for documentation. The International Bureau of Weights and Measures (BIPM) is the gatekeeper of these definitions. If you are a manufacturer in Germany shipping sensors to a lab in Japan, your calibration certificates must use "Celsius." Using "Centigrade" can actually lead to legal or compliance issues in high-stakes industries because it isn't the recognized SI unit name.

Actionable Takeaways for the Everyday User

If you want to sound like an expert and stay current with modern standards, here is how you should handle these terms:

👉 See also: Why Factory Resetting a JP5 Mini is Actually Necessary Sometimes

• Phase out Centigrade: Stop using it in professional emails, school papers, or technical discussions. It marks you as someone using outdated information.
• Check your sources: If you see a thermometer labeled "Centigrade," it’s likely an antique or a very old piece of equipment. Be aware that its calibration might be off by modern standards.
• Capitalization matters: "Celsius" is a proper noun (named after a person), so it should always be capitalized. "Centigrade" is a common noun, but since it's obsolete, you're better off just avoiding it.
• Understand the "Degree" symbol: In Celsius, there is traditionally a space between the number and the degree symbol in some styles (e.g., $25\ ^{\circ}C$), but the most common international standard (ISO 80000-1) suggests no space between the degree symbol and the letter C.

Switching your vocabulary to "Celsius" isn't just about being pedantic. It's about aligning with the international scientific community that decided, nearly 80 years ago, that we needed a single, unambiguous name for how we measure the heat of our world.