100% is the change from 128 to 256
Calculation steps:
[( 256 - 128 ) ÷ 128] x 100 = 100%
Formula
Percentage change = [(256 - 128) / 128] x 100
Subtract the new number by the original number
256 - 128 = 128
128 ÷ 128 = 1
1 x 100 = 100%
Example