Exporting Jpeg from Photoshop becomes Larger size on macOS

They are both the same size! The difference is the PPI tag which is just metadata. 

They are both (on one axis) 2550 pixels. But one divides 2550 by 72 and the other by 300. Meaningless really. What counts is the total number of pixels over HxW. 

Old but still nothing has changed in terms of how this works:

http://digitaldog.net/files/Resolution.pdf

The file size in pixels has not changed. What has happened is the conversion from pixels to a physical size.

In your original it used 300ppi to work out the physical size. When exporting an image (as opposed to saving) that ppi data is stripped out (it is just a number stored alongside the image). On re-importing, Photoshop has to use something to calculate the size in inches (or cm) and, in the absence of any ppi data uses 72ppi. That makes the same pixel size look physically bigger.

Dave

Hi,

We're sorry about the trouble with the image size. Would you mind telling us which version of Photoshop are you working on along with your computers macOS version? Are you opening the exported Jpeg in the image viewer of your Mac or a different application? If you open the exported Jpeg back in Photoshop, then go to Image > Image size, what are the dimensions that you see there?

We're here to help, just need some more info!

Regards,

Nikunj