Who Invented Fahrenheit and Celsius? The Rivalry Behind Temperature Scales
Two men, two temperature scales, two very different legacies. Daniel Fahrenheit and Anders Celsius both solved the same problem — measuring heat — but their solutions divided the world for three centuries. Here is the full story.
Temperature is one of the most fundamental measurements in daily life — weather forecasts, cooking, medicine, and engineering all depend on it. Yet the world is split between two scales that use completely different numbers for the same physical reality. A comfortable summer day is 25°C or 77°F. Water boils at 100°C or 212°F. Understanding why two scales exist, and who invented them, requires going back to the early 18th century.
Before Fixed Scales: The Problem of Temperature
For most of human history, temperature was described qualitatively: hot, warm, cool, cold. The thermoscope — a device that showed temperature change through the expansion of liquid — was invented around 1593, often credited to Galileo Galilei. But thermoscopes had no fixed scale, so readings from different instruments could not be compared. A measurement was only meaningful relative to other measurements on the same device.
The challenge was agreeing on two fixed reference points — a cold anchor and a warm anchor — from which a numbered scale could be built. Different inventors chose different references, which is why we ended up with competing systems.
Daniel Gabriel Fahrenheit (1686–1736)
Daniel Fahrenheit was a Polish-born Dutch physicist and instrument maker who spent most of his life in the Netherlands. He invented the mercury thermometer in 1714 — a major improvement over alcohol thermometers because mercury expands more consistently and reaches higher temperatures without boiling.
For his scale, Fahrenheit chose three reference points. Zero degrees was set at the temperature of a mixture of ice, water, and ammonium chloride salt — the coldest temperature he could reliably reproduce in his laboratory. The second reference point, 32°F, was the freezing point of pure water. The third, 96°F, was an approximation of human body temperature (later refined to 98.6°F after the scale was extended).
Why these odd numbers? Fahrenheit wanted a scale fine-grained enough to measure body temperature precisely without requiring decimal fractions — a practical concern for medical use in an era before calculators. The resulting scale, with 180 degrees between freezing and boiling water, gave him the precision he needed.
Anders Celsius (1701–1744)
Anders Celsius was a Swedish astronomer at Uppsala University who proposed his temperature scale in 1742. His original scale was inverted from the modern version: he set 0 as the boiling point of water and 100 as the freezing point. This was reversed after his death — by Carl Linnaeus, the botanist, among others — to the scale we use today, where 0°C is freezing and 100°C is boiling.
The elegance of the Celsius scale is its alignment with water's properties: 0 and 100 are easy to remember, easy to reproduce, and directly meaningful for everyday life in temperate climates. The 100-degree span between freezing and boiling water fits naturally with the decimal system.
Which Countries Use Fahrenheit?
Today, Fahrenheit is the primary temperature scale in only five countries: the United States, the Bahamas, the Cayman Islands, Liberia, and Palau. Every other country in the world uses Celsius for weather, medicine, and daily life. Even in countries with historical ties to the UK — Australia, Canada, India, New Zealand — Celsius has been standard since metrication in the 1960s–70s.
The UK itself switched to Celsius for official weather forecasting in 1962, though many older Britons still think in Fahrenheit and the media often reports both. The transition in the US has never been attempted at a national level.
Kelvin: The Scale Physicists Use
In 1848, British physicist William Thomson (later Lord Kelvin) proposed an absolute temperature scale based on the theoretical concept of absolute zero — the point at which all molecular motion stops. Absolute zero is −273.15°C or −459.67°F. The Kelvin scale starts at absolute zero (0 K) and uses the same degree size as Celsius, making conversion simple: K = °C + 273.15.
Kelvin is the SI base unit for temperature and is used universally in physics, chemistry, and engineering calculations. It has no 'degree' symbol — temperatures are written as 300 K, not 300°K.
Converting Between the Scales
- °C to °F: multiply by 9/5 (1.8), then add 32 — e.g. 20°C = (20 × 1.8) + 32 = 68°F
- °F to °C: subtract 32, then multiply by 5/9 — e.g. 68°F = (68 − 32) × 5/9 = 20°C
- °C to K: add 273.15 — e.g. 100°C = 373.15 K
- Quick estimate: double the Celsius value and add 30 for a rough Fahrenheit — e.g. 25°C ≈ 80°F (exact: 77°F)
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