There are no rules, but I would hang them to just below the top of the mirror......Maybe 3" to 4" from the top of the mirror to the bottom of the light fixture.

Bungaloonie, really love the look you have going on. Is that vanity from Costco? If so, I have the same one that's been in storage waiting to be installed in one of my guest bathrooms. Do you have a picture from further back of the full vanity? I'm curious how you finished it flushed or how it looks since it's technically a freestanding vanity. In regard to your question, I agree with Lampert Dias Architects, Inc. I would hang them so that the light fixtures are just below the mirror.

Jen K, thank you for the words of encouragement! The pendant is from Lowes. And yes, laughing has been getting us through a lot of this remodel! Hahaha!

Lampert Dias Architects, thank you for your expertise. Your help is so appreciated. And especially thank you for the specificity of your answer. I would have been making the DH balance up there indefinitely, lowering and raising the sconces by an inch here and an inch there! :)

Chris Smith, good eye! That is a Costco Vanity that we have had in the garage for a year and a half. We saw it, and scooped it up immediately. Hard to believe it has the real marble top, heavy duty wood base, soft close doors, etc, at the price it was! We will be changing out the hardware though, to better coordinate with our vintage style, chrome fixtures we got from Kohler. We tiled up a bit higher all around the entire bathroom, to accommodate the vintage style faucets, so we didn't use the marble backsplash that came with it. I included pics of the base from the front. The drop cloth is already in place to get up there and hang those sconces. I hope that answers your question. :)

bungaloonie, that looks awesome! I really like your use of materials with the subway & marble tiles and pendants.

Usually 36-40" from the bottom of the pendant to the counter on the vanity is a good place to start and then adjust from there.