What is the formula to convert the result of an 8-bit ADC to voltage?
(2.5/6)*255=106.25 is the correct formula.

You can check with:


sensed 0 => code 0
sensed 6V => code 255


and 2.5V is just above 1/3rd of the way, so code 100 of 255 looks correct (255/3 = 85)

6/255 = 0.0235 also has a meaning, it's the V/code value, to get back the sensed value from the code (106*0.0235 = 2,491V)