There's a much easier way in Photoshop to designate file size to whatever size you want. Use Save for Web and click on the little down arrow to the right of the Preset dropdown, choose Optimize to File Size, and enter the desired size. No guesswork that way.
*or do it like Gene shows in the above post.
I must have missed this one, thanks it also definitely seems like another easy way to do it. I will be using this method and the other one in light room depending where I edit, thank you!