Understanding Export Quality Settings in Lightroom Classic

[MelodyanneM]

I'm having a hard time understanding if I should let the image sizing box do its own thing or if I should manually enter 300dpi for every photo I want to export for printing. The pixel count doesn't change so will changing the dpi make a difference in print quality?

[TheDigitalDog]

That 300PPI is kind of meaningless as it's just a resolution tag. The number of pixels is key here. Work in pixels. 

1000x1000 pixels at 1000dpi and 1000x1000 pixels at 10dpi are the same. See this old article that to this day still applies:

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

Then in terms of ideal resolution for some print work, see:

https://www.digitalphotopro.com/technique/photography-workflow/the-right-resolution/

[MelodyanneM]

Thank you!

[dj_paige]

... or if I should manually enter 300dpi for every photo I want to export for printing.

You can't enter 300dpi (dot per inch) in the Lightroom Classic Export dialog box. You could enter 300ppi (pixels per inch) but there are two extremely different things — dot per inch meaning how many dots of ink a printer will use per inch, and pixels per inch, meaning how many pixels of the photo get printed per inch. These both are entirely meaningless if you are not going to print anything. They do not affect digital images. They only affect printed images. And if you are going to print something, you can only control ppi from Lightroom Classic.

[MelodyanneM]

I should possibly clarify. I'm exporting as jpeg to have printed by a
professional lab. It says dpi not ppi in the dialog box. Hence my question.
I do understand the difference between the two. I'm just not clear on what
are the best settings to export a jpeg for printing.

Melody M

[MelodyanneM]

My apologies, I do see now that it is ppi so then indeed it is meaningless when it comes to printing is it not?

[MelodyanneM]

My apologies I see now that it is indeed ppi in the dialog  box but when I look at the file properties it is labeled as dpi and that does change based on what I entered in the ppi dialog box. So still not sure what I should be doing but it seems to me letting Lightroom do its own thing there is reasonable.

[TheDigitalDog]

What size print do you want?

How many pixels do have?

[MelodyanneM]

Pixels vary based on how much cropping was done. I'm trying to figure out
how big I can print.

Melody M

[TheDigitalDog]

Crop as desired and use the info overlay set to pixels and you'll know exactly.

[DS256]

"Pixels vary based on how much cropping was done. I'm trying to figure out
how big I can print." LrC will attempt to enlarge an image that is smaller than the requested export size. The 'Do Not Enlarge' prevents this from happening.
You may want to explore some on-line pixel to print calculators like the following. Note that the distance the print is being viewed from is one of the parameters https://www.omnicalculator.com/other/pixels-to-print-size

[DS256]

"I'm having a hard time understanding if I should let the image sizing box do its own thing or if I should manually enter 300dpi for every photo I want to export for printing" My understanding is that the RESOLUTION option only comes into play when you are selecting a physical dimension in the export. For example, in the  following, I select 8x10 inches.

The resulting image is 2400 (10x240) x 1690 (240x8=1920 but it's cropped) pixels.