And to measure the temperature, mercury thermometers are often still in use. So today we are used to water freezing at 0 degree Celsius and water boiling at 100 degrees Celsius.

He chose the melting point and boiling point of water as fixed points for the temperature scale and divided the change in volume of mercury between these points into 100 equal parts. Anders Celsius, a Swedish astronomer, mathematician and physicist, defined this temperature division named after him, 'degree Celsius', in the 18th century. The common unit for temperature in German-speaking countries is measured in degree Celsius (☌). −31☏ is within the one-degree range from (and is equal to) the true value of −31☏.Calculator ↑ Contents ↑ Degree Celsius (☌).90☏ is within the one-degree range from the true value of 89.6☌.Įxample #2 (Temperatures Lower than 10☌):.If the original temperature is below 10☌, add instead of subtracting.Įxample #1 (Temperatures Higher than 10☌): Subtract the sum you remembered earlier.Multiply (the original temperature) by two.If the original temperature is below 10☌, use the higher nearest multiple, not lower. For each five degrees from 10☌ (up to the lower nearest multiple of ten), remember one (sum the ones in your head but do not use this sum yet).The method for reverse conversion seems a bit trickier but is not really it. −10.5☌ is (almost) within the one-degree range from the true value of −9.4☌.25.5☌ is within the one-degree range from the true value of 25.6☌.Įxample #2 (Temperatures Lower than 50☏):.Add one for each: 60, 70, 80 Gives 81.Now you have degrees Celsius plus–minus one degree.Įxample #1 (Temperatures Higher than 50☏):.If the original temperature is below 50☏, use the lower nearest multiple, not higher, and subtract instead of adding. For each ten degrees from 50☏ (up to the higher nearest multiple of ten), add one.In addition to the Subtract-Thirty-Divide-by-Two rule (for Fahrenheit-to-Celsius conversion), also memorize that 50☏ is 10☌ then you are ready for conversion. ⚠️ So here goes a warning: The method below is generally unsuitable for body temperatures. For body temperatures, you would usually want to memorize critical temperature points instead both for Fahrenheit and Celsius (e.g., using a chart like this one ).īy contrast, the method is perfect for rapid conversion of air temperatures in everyday life. The method outlined below is only slightly computationally heavier than the crude one but has the precision range of around one degree. The crude method is imprecise with error as high as a dozen degrees at extreme outdoor temperatures. Now you have degrees Fahrenheit plus–minus several degrees.Vice versa for reverse Celsius-to-Fahrenheit conversion: Now you have degrees Celsius plus–minus several degrees.

Calculator f celsius