Making text size proportional on images in photoshop

Thank you everyone for your tips and suggestions. Very helpful!

How do you have Type set in Preferences?  Set it to a linear size like millimetres.  Avoid Points which can lead to problems with very large pixel size canvas

Set Rulers to the same unit (mm) by right clicking inside either ruler.

With these settings, no mater what the pixel size of the image, if the rulers show it to be — for instance — 150mm or 15cm, and you create a type layer of 10mm, you know it is one tenth the height of the canvas.

​Note: the rulers below are set to mm

[EDIT]  If you want to do this with an Action, and have the same relative placement (position) with different image/canvas sizes, then I then the trick is to have the rulers set to Percent when you record the action

I am guessing the above answers are correct.  Look at the size and resolution on each image and make sure they are the same.  That could be the issue.

If not let us know.

If you have different resolutions (Image > Image > Size > Resolution) it can make the difference. For text to appear visually the same in size you must pay attention to the resolution, For example: type size 10pt in document with 300 ppi resolution must be set to 42pt in the document with 72 ppi to appear same in size (dimensions or space which occupies on screen).

Either ensure that all your images have same resolution or change text size manually.

Check the each of your banners are the same size and resolution.   Text size is relative to resolution or size I believe.