I have hundreds of files that were originally 1,000 px x 1,000 px, with a resolution of 300. All of

@Wendy295489809sno 

The PSD file attached has a resolution of 1000 PPI and a canvas size of 1000px square (both Photoshop and ExifTool agree).

1" square at 300 PPI would equal a 300px square canvas, much smaller than 1000px.

Uncheck resample and change the ppi number to whatever you want. As long as you're not resampling, nothing in the file changes. The file itself is just pixels; the ppi number is metadata that can be changed.

Hi @Wendy295489809sno. The .png file you attached has a size of 1000 x 1000 pixels at 72 ppi. If the file was resampled to 300 ppi, the size would be 4167 x 4167 pixels. Is that what you started with? Can't you simply change it to what you want: