The Adobe article you linked to unfortunately contains misleading, and even wrong information.
This is how PPI and DPI works:
PPI (Pixels Per Inch) is an image property – the number of image pixels used to print one inch on paper.
Pixel dimensions divided by PPI = Printed dimensions in inches.
You set the PPI in the Resolution field when exporting from LrC.
The PPI value tells you nothing about image size, pixel dimensions do. But it does tell you what size the printed image will be if you do the math.
PPI and DPI are often confused, and many people use DPI when they should be using PPI. Even Windows gets this wrong.
DPI (Dots Per Inch) is a printer property – the number of ink dots a printer uses to print one inch one paper.
The article claims that images have a DPI resolution, but they don't. The resolution for an image is always PPI.
The DPI is set in the printer driver, and is typically much higher than the PPI value of the image.
I routinely make 33 x 44" prints on my own printer at 180 PPI. Using a higher value does not improve image quality. (and it also requires more pixels, see the formula above)
In the printer driver I set the DPI to 1440. Lower values (720 or 360) lead to reduced image quality.
I've just switched to Lightroom Classic and am learning my way round it. When I export the very same RAW image it yields a 96 DPI and the file size is only around 7 MB - both values suggest it is a less detailed image.
Where are you seeing a PPI value of 96? If you export at 300, the value should stick.
The file size of a jpg is determined by three factors:
Pixel dimensions
Quality setting used when exporting
Image content
Assuming that the first two are identical, the file size can still vary a great deal, depending on image content.
An image with predominantly smooth, flat or out of focus areas will compress well, leading to a relatively small file size.
An image with lots of sharp, busy detail (or noise) will be much harder to compress, leading to a relatively large file size.
40 kb, exported at Quality 80
146 kb, exported at Quality 80
So the file size of a jpg is not an indicator of image quality.
The only way to determine the quality of any image is to view it at 100%.
At this magnification, one screen pixel is used to display one image pixel, giving you a true representation of the image.
Any other magnification will be inaccurate and misleading because the image has been scaled.
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