16x9 Photo Conversion

I have a standard sized photo taken with my Nikon DSLR and would like to convert that image to a 16x9 cinematic aspect ratio. I did this no problem in Lightroom but I would like to add the black bars on top and bottom to make it more cinematic. My question is what size should the image be with the black bars on it? Is it 16x9 with or without black bars?

The black bars are to display a 16x9 picture on a standard screen that is taller than that ratio. You don't add the black bars to make it 16x9. In your editing you either stretched (distorted) the "ordinary" picture to make it 16x9 or you chopped off from the top and/or bottom to give the ratio.
So your question is just confusing at this point.

When you crop a standard image which came from your camera with a 3:2 aspect ratio and then crop it to a 16:9 image aspect ratio there's really no need to add any black bars, top and bottom to make the image fit into a old standard motion picture or television aspect ratio of 5:4 or 4:3 image aspect ratio

You of course can create a new canvas in Photoshop which has an image aspect ratio you like and use it as a background layer. You can make that layer black and then place your cropped image within the width of that new canvas, adjusting it until you have equal size bars, top and bottom, merge the two layers and name it something other than the original file name.

I guess it would be an interesting exercise for someone learning how to use Photoshop, but not one that must of us would do, sine most of us are Photographers and spend our time making sure that the images that come from our cameras are as close to what we envisioned without resorting to using Photoshop.

Try searching YouTube for tutorials which will show you how to create what you hope to produce