Your syntax is basically correct. The only thing I might add is to be sure of type casting your data correctly. For example, I opened a Landsat 5 image and its data values are in byte. I would want to make sure I perform this calculation in floating point precision: float(b1)/mean(float(b1))*100 In the next dialog of Band Math, you will pair the variable 'b1' to the appropriate band. Since you wish to do this for every band in the file, instead choose 'Map Variable to Input File' and select the file name. This will apply the equation to each band in sequence and return all bands in a single file. Is this what you were looking to do?