Bradford assay is typically given in terms of absorbance units (AU) at a specific wavelength, commonly 595 nm.
To convert the Bradford assay result into a percentage of protein, you need to establish a standard curve using known concentrations of protein. In this, Plot a graph of absorbance (y-axis) versus protein concentration (x-axis) for the standard solutions (at least 5 known samples). Once you have the protein concentration of your know sample, you can calculate the percentage of protein.
Divide it by the total protein content (in mg or µg) of the sample.
Percentage protein=Protein concentration of sample / Total protein in sample×100