If you have stained gel image analysis software, you can draw a box around the purified protein band and a box around the entire lane. The percentage purity can then be expressed as the amount of stain in the purified protein band divided by the total stain in the lane x 100. You should use a gradient or high percentage gel to be sure that none of the proteins run off the gel, and a moderately heavy loading to be able to detect the fainter bands. You should stain with Coomassie Blue or with a fluorescent protein stain, but not silver stain.

Try using a PAGE analysis software. You can use it to calculate protein volume based on the intensity of the bands, comparing them to a standard.

If you have stained gel image analysis software, you can draw a box around the purified protein band and a box around the entire lane. The percentage purity can then be expressed as the amount of stain in the purified protein band divided by the total stain in the lane x 100. You should use a gradient or high percentage gel to be sure that none of the proteins run off the gel, and a moderately heavy loading to be able to detect the fainter bands. You should stain with Coomassie Blue or with a fluorescent protein stain, but not silver stain.

Just an addition, one of the software it called "imageJ" it works quite well.

I am agree with Peter, use "Image J". It will be really helpful for your purpose.

This is link for Downloading:

https://imagej.nih.gov/ij/download.html