The formula to convert degrees Fahrenheit to degrees Celsius is:

$$ C = (F - 32) / 1.8$$

So, to convert 28 degrees Fahrenheit to degrees Celsius, we have:

$$ C = (28 - 32) / 1.8 = -2.22 $$

Therefore, 28 degrees Fahrenheit is equal to -2.22 degrees Celsius.