What is the correct resolution to save images for online? (retina)?

File size is the important variable, less than 100K means people can't steal your images and print them.

If you save at 2880X1800 pixels they are printable files. For security always save at around 1000 pixels on the longest edge, and even then they can be printed small.

The screen even on retina screens is not 220ppi, that's just the default ppi for Raw files, set for print, jpegs are always 72ppi because that's all most screens can display you need more bit depth to display a higher ppi, not more resolution. Most screens are only 8bit, some laptop screens are even worse at only 6+2bit, for image and video editing 12bit or even 16bit which will cost the same as a small car, is visibly better. There's more to the spec of screens than the number of pixels, important though that is.

PPI is a variable, it just alters the size the image is shown, every time you zoom into an image on screen your altering ppi. Ppi works by altering the size of each pixel, it does not alter the file data, just how it's viewed.

File size is important to the server too, which is why they limit you to 1000 pixels, larger files need more disk space.

Chris

"ppi" is irrelevant. Computer displays (including iPads) work in pixels, not "ppi."

You can save files for the internet at whatever resolution you want to.

Here's the thing to consider: many people still don't have high-speed internet, nor do they have high-resolution displays. If you don't care about how those people see your images (slow to load and way too big for their screens), then save a high resolutions. If you do, then save at lower resolutions. It's your choice. If this is for a web site that you expect to attract a lot of traffic, then not only will higher resolution images frustrate a lot of visitors, you might exceed your ISP's bandwidth stats, and either get shut down or have to pay a higher fee.

No the image continues to be medium determination for the time of the full technique. whilst that's outlined out, that's outlined as a medium determination image. once you're taking a image, you're nonetheless viewing the medium determination image. in case you re-test the image at medium determination it might make the image even worse. you may might desire to verify at a extreme determination for the image to maintain its high quality. once you resize the image, its gonna pixelate, whether you do all that and resize, or merely resize.

Save it less than 100 k