I will start with some examples:
In most cases we say: it is twice hot as yesterday, it is twice hot than last week. When we refer in this way, we think at temperature as being normal at 15 degrees celsius, acceptable at 25 and hot over 30. If yesterday were 25 degrees, we can say that today is twice hot than yesterday with only 33 degrees celsius, 33 is not double of 25, but we say it, because we don’t think in degrees, we think just how hot our skin feels.
The answer of the question in this topic is found in math, the formula for converting celsius to fahrenheit is multiply by 1.8 and then add 32. In this way it is clear that doubling both values, we won’t get a doubled result, because we have that +32, which is always constant.
F = C * 1.8 + 32