One degree on the Fahrenheit scale is only 5/9 as large an interval as a degree on the Celsius scale, so a change in temperature is 1.8 times as large in Fahrenheit. And the scales are offset by...
To convert from degrees Celsius to degrees Fahrenheit, multiply the number by 9, divide by 5, and add 32. In this instance, -11.5 degrees Celsius is equal to -11.5 x 9 = -103.5/5 = -20.7 + 32 = 11.3....
The two temperature scales do not have the same unit size. The difference between 80 and 90 ºF is not the same size as between 80 to 90 ºC. Celsius = (Fahrenheit - 32) x 5/9