As you may have seen in other discussions, we often need more information to answer your question...
The purpose of the contact sheet is to show a smaller version of many images (in the old times, it was negatives on a sheet of Photographic paper, small 35mm images) in a single page.
If a file changes size when going from a document to another, it is because the number of pixels per inches(PPI) is different. (a 600 pixels wide image will "measure" 3 inches on a 200PPI document, but only two inches in a 300 PPI one.
Could you tell us what you are trying to do, so that we can direct you to the best path to do so?
What version of the contact Sheet script are you using, in which version of Photoshop?
I'm bringing in buckie22's response here:
Thankyou for your response PECourtejole.
I'm using version CS6 I use to have CS4 never had this problem where the image reduces to about a third of the size when being dragged on to new page.
I am doing the same as always open new page 200ppi change picture to 200ppi, (change picture to tiff file same a new page).
Also tried them all at 300ppi still picture appears on sheet approx one third smaller then actual size
Example:open new page A4 page 210x297mm at 200ppi - Photo size 100x110mm at 200ppi when photo is dragged on to A4 page
image appears on page approx 40x45 millimetres.