I see questions from time to time about web posting of digital images. There is a lot of confusion out there about the size of an image, the resolution of an image and "weight" of an image (meaning the amount of space it takes on hard drive or any other storage media). I suggest you read this as a starter:

https://www.picmonkey.com/blog...-size-and-resolution

If you read the article from the link, then you see that the pixel dimensions aren't the only thing contributing to image quality as perceived on a screen, or on paper. Use a simple rule of thumb: for prints consider 300 dots per inch (DPI) as your density of pixels, for computer screen use consider 96 pixels per inch as your pixel density. This is easily chosen in the different photography softwares when sizing images. Lastly, make sure you have imbedded the sRGB color space (also known as ICC profile) for web use and not Adobe RGB. The vast majority of computer screens cannot display the full gamut of Adobe RGB, usually resulting in duller looking images.

If you follow these simple rules of thumb, your images will appear better and won't be any "heavier" than necessary.

AR doesn't have stringent constraints on image size and resolution, but I have found that on the horizontal axis 1200 to 1500 pixels allows the image to fit on most monitors. For pictures in portrait (or vertical) orientation the long vertical size should be limited to 800 to 1000 pixels. If greater they usually can't be viewed in their entirety, requiring that you scroll your monitor to see them.

Of course, I learned all this the hard way.

My brother-in-law is restoring an old Cadillac and when some friends from Argentina visited they all wanted to get in and have pictures taken. This shot is 1500 pixels on the long side and in Lightroom I set the "export" sizing as 315 Ko maximum. So, it should be visible on most monitors and only takes up 315 Ko of space. Taken with my 105mm. I also share photographs on a web forum mostly about photography and 315 Ko is their maximum size allowed, so I just use that size in general. I don't think there is anything special about 315 Ko.



There is another reason why you might want to use low-resolution images when posting on internet, which is image theft. Suppose you take the picture of the century. If you post a full resolution image it can easily be stolen and used by others to sell to stock photo agencies or even to sell prints. A low resolution image reduces the chances that will happen.

I usually use Lightroom to resize my photo files for web posting. This is the dialog box when I want to "export" from Lightroom:



As you can see, I have the option to limit the file size (which I have set to 315 Ko), or, I can "unclick" the Limit File Size box and use solely the Image Sizing box with a long length specification and a pixels per inch box, which I set at 96. Not all softwares have a specific "Limit File Size", which means you will have to play around with an image "quality" dialog box until you get the low-resolution image you want.

As an example, image file size of the picture of the Cadillac is under 315 Ko, the image size of the screenshot of the Lightroom dialog box is 1.5 MB, about 5 times larger, since I didn't reduce it.