A point (
pt) is a physical size and it depends on the document resolution. I imagine between two your documents it’s not the same.
Select your first document, go to
Image > Image Size to get its
Resolution, then switch to the second one (the one you want to change) and in the same window change the
Resolution value to the same as your first doc.
And make sure
Resample is turned off, otherwise the dimensions of the document will also change.