20% is the change from 255 to 306
Calculation steps:
[( 306 - 255 ) ÷ 255] x 100 = 20%
Formula
Percentage change = [(306 - 255) / 255] x 100
Subtract the new number by the original number
306 - 255 = 51
51 ÷ 255 = 0.2
0.2 x 100 = 20%
Example