To convert from Fahrenheit to Celsius degrees, fist subtract 32 (freezing point of °F - freezing point of °C; that is 32 - 0 = 32), then divide the result by 1.8 because it is the ratio between °F and °C.
For example, to convert from 77 °F to °C, subtract 32 from Fahrenheit first and then divide by 1.8 ratio, that is: (77 °F - 32) / 1.8 = 25 °C .
The "1.8" Celsius to Fahrenheit ratio means there are 1.8 Fahrenheit degrees for each Celsius degree and it is calculated by dividing the difference between boiling and freezing points for each of these temperature scales, that makes (212 °F - 32 °F) / (100 °C - 0 °C) = 1.8 .
Fahrenheit is a temperature scale with the freezing point of water is 32 degrees and the boiling point of water is 212 degrees under standard atmospheric pressure (101.325 kPa). The absolute zero temperature is -459.67 °F. The symbol for Fahrenheit scale is "°F".
Celsius (centigrade) is a temperature scale with the freezing point of water is 0 degree and the boiling point of water is 100 degrees under standard atmospheric pressure (101.325 kPa). The absolute zero temperature is -273.15 °C. The symbol for Celsius scale is "°C".