There are three temperature scales commonly in use today: Fahrenheit, Kelvin and Celsius — which is Kelvin at its heart, but on a different number range. Sometimes you’ll see debates online on which system is better, and interestingly you’ll even see proponents of the US switching to metric make an exception for the continued use of the Fahrenheit scale. Defense of Fahrenheit is made in the face of the far-reaching use of Celsius and Kelvin across the globe. So, which system is better? What are the differences? Here’s a little background information about each:
Fahrenheit is commonly used for most things in the USA, its unincorporated states (including Puerto Rico, Guam and the US Virgin Islands), the Bahamas, Belize, and the Cayman Islands. In Canada, it’s the most common scale used in oven temperatures and a small percentage use it for outside air temperature. In the UK, it still has some usage in the media — especially at summer-time when temperatures reach the high eighties or into the nineties.
It is based on a scale proposed by Polish/Dutch physicist Daniel Gabriel Fahrenheit in 1724. He based the zero-point of his scale on a mixture of ice, water, and ammonium chloride. This is a ‘frigorific mixture’, meaning its temperature stabilises automatically, independent of starting temperature. After various calibrations, he set the melting point of ice (at standard pressure) at 32º and normal body temperature at 96º, making 64 intervals between them, which meant he could mark degrees in his thermometer by dividing the intervals by 2, six times. Given advances in science, normal body temperature is now redefined as 98.6ºF. In this scale, the boiling point of water is at 212º, making exactly 180º between the melting and boiling points of water at standard pressure.
What are the advantages of this scale?
- It is generally better suited for measuring air temperature. In this scale, 0 is a very cold day, 50 is mild and 100 is a very hot day. Obviously, in extreme cases, temperatures can go above and below these values, but as a rough guide — Fahrenheit is like a percentage scale of how warm the air temperature is, making it ideal for weather reporting.
- With Fahrenheit you get more granularity between whole numbers than you do with Celsius or Kelvin. It’s generally considered that outside of polar regions and deserts, temperatures typically range from -20°F to 110°F — a 130º range. That range is about 72º in Celcius (-28.8 – 43.3). Fahrenheit gives you 1.8 times the precision between whole numbers.
Celsius is the most common temperature scale used across the globe. In everyday use, it is used for air, water and body temperature. In science it is used alongside Kelvin.
It is named after Swedish astronomer Anders Celsius (1701–1744). Prior to being renamed, it was previously called centigrade (from the latin centrum (100) and gradus (steps)). Celsius is an SI derived unit, meaning it is based on the SI unit of temperature — the Kelvin, but not one of the SI base units itself. It was originally based on the freezing and boiling points of water at standard pressure (0 and 100 respectively) which now translates to 273.15 K and 373.15 K exactly. Kelvin is based on absolute zero — the lowest temperature possible, or where a medium contains absolutely no energy. One degree increment in Celsius is equivalent to a 1 K increment.
What are the advantages of this scale?
- It is generally better suited to measuring water temperature. At standard air temperature, the 0–100 scale works well when you are concerned with water temperature, such as if ice will form outside or at what point milk will boil in your saucepan (milk is mostly water).
- Given that it’s the most widely used temperature scale around the world, and that it’s used in science (alongside Kelvin), if communication with people in other countries is needed, then Celsius or Kelvin is yer man — especially in the science world.
I’ve always understood the Celsius scale as it’s what I grew up with, but have come to understand Fahrenheit from conversing with U.S. colleagues and can see the benefits of the latter.
We mostly use our thermometers for air temperature (do I need a coat or not), surface water (will I need to defrost my car or not), body temperature (am I running a fever or not) and oven temperatures. For air temperature, the most common use of temperature, and body temperature I think Fahrenheit wins out, because of the neater 0–100 range for air temperature and the greater granularity. For measuring water, Celsius wins as it has a neat 0–100 range — although those values change for people on a mountain, down a valley or just not at sea level. For oven temperatures, I don’t think it makes much of a difference either way.
Neither scale is perfect, but in general I think Fahrenheit is better for everyday things like air temperature and Celsius is better for water temperature and science. I don’t think the switch to Celsius has made much tangible difference to everyday life in the UK, Ireland, Australia etc and as such I don’t see any strong reason for the USA to take on the cost and hassle of making the switch to Celsius outside of science.