does reducing pic size reduce quality?

[Nikonian]

even after i convert my adjusted raw files to jpg they are still close to 20mb some of them

this takes way too long to upload on Facebook and elsewhere so i usually downsize them

i doubt anyone on FB would notice as Facebook compresses them anyway, but, does reduction in picture size reduce quality as well?

they are still sizable, about 6 or 7 mb and around 4200 x 2800 give or take

[Matt]

Yes, reducing size reduces quality, but a 20mb file has much more information that can be displayed on a monitor anyway. If all you are doing is sharing through social media, you can reduce the image to 1200 pixels on the wide side and that is plenty for almost any monitor. Go to 2,000 pixels if you want. For an 8x10, that is is only 5 MP, and a jpeg at that. Save at a medium-high quality and you should not be more than a few 100 kb.

Of course, you can't go back and print this file without losing quality, so make sure you keep the higher resolution files as well.

[Mike1942f]

Yes, it reduces quality, how much depending on how you do it, so you always keep an original that is the max size you want to keep but the pictures you are uploading now are way too big and unless you really want people to enlarge and scroll them (where they can) there is no point.
For example, your 4200 even if put across a 2048 screen would be twice too big and cutting it to that size would reduce the storage size to about 1/5th the current, if not lower.
Take a look at some of the images on Facebook (I am not there) and right click and look at image properties (or image info) for the size - you don't really need to upload anything bigger.

[Steve P]

Yes, but for online display, it is a moot point. It will still look just fine. For online use, you should size the photo to about 800 pixels on the longest side, 72ppi resolution, and Jpeg compression at 5. That cuts WAY down on quality for PRINT purposes, but is ideal for online viewing and savings of bandwidth. Set it up as above, and Facebook will do no further butchering of the photo.

steve