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Why does the US use Fahrenheit instead of Celsius? What are the differences?

99 percent of countries on Earth use Celsius to measure temperature, but the US doesn't - why?

People were evacuated from their homes after a wildfire reached residential areas of northern Athens as record temperatures reached 42 degrees Celsius (107.6 Fahrenheit) in the Summer
Milos BicanskiGetty Images

Arbitrary, and for most of the world very confusing, Fahrenheit temperature measurement is a rod the US uses to beat its own back. Never mind the only other places that still use the measurement are the Cayman Islands and Liberia, it makes no sense that one of the world's largest countries should use a measurement that is difficult to read, and not even mathematically precise, leading to an embarrassing $125 million mistake back in 1999.

A conversion mistake between the two scales led to a Mars rover being destroyed; Fahrenheit has an inbuilt error that makes a perfect conversion impossible. So why is the US stuck to its old and outdated way of measuring heat?

What is the history behind the systems?

Fahrenheit is named after Daniel Gabriel Fahrenheit, a German scientist born in the Polish-Lithuanian Commonwealth in 1686. He was the first person to create a reliable way to consistently tell the temperature.

Fahrenheit set zero at the lowest temperature he could get a water and salt mixture to reach. The second fixed point in the system was the temperature of the human body, 96 degrees, but his measurement was slightly off. This set the boiling point of water at 212 degrees, and the freezing point at 32 degrees.

The British liked his ideas and, after inducting him into the Royal Society in 1724, the measurement was proliferated around the globe as the British Empire expanded.

However, the invention of the metric system but thermometers back under microscope. The French Revolution inspired an overturning of the old ways, and Fahrenheit was thrown out. It helped that the change stuck; it makes sense that the zero temperature is the freezing point of water, with 100 degrees as the boiling point. Both can be easily visualized as ice and steam, but Fahrenheit has no visual cue for what the temperature is.

Even the British changed their waves, mostly at least, in 1965, and the US was very close to following suit.

Why hasn't the US changed to the metric system?

In 1975, Congress passed a law that was supposed to begin the process of metrication. It set up a Metric Board to supervise the transition.

However, as it made metrication voluntary, rather than mandatory, people simply chose not to learn the new systems for temperatures and weights.

"Motorists rebelled at the idea of highway signs in kilometers, weather watchers blanched at the notion of reading a forecast in Celsius, and consumers balked at the prospect of buying poultry by the kilogram," Jason Zengerle writes in Mother Jones.

So the US still uses Fahrenheit, and there have been no major attempts to change it since.


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