No rule. Posting photos of your space would get you more relevant advice.

file:///var/mobile/Library/SMS/Attachments/a6/06/775C8B0A-4A2D-4772-B3C4-B0D9AEE4DC8E/IMG_9129.HEIC

I’m not sure the attachment worked. If not, I’ll try to work on it tomorrow.

https://share.icloud.com/photos/060fvMWcYHT3kNiumJi6ogZvQ

Please use j pegs?

You have a 46" vanity in an alcove.

Where is your lighting going? Do you want a fixture over the mirror, sconces alongside the mirror? What is the ceiling height? What is the finish of the vanity,,,,, Do you have an inspo pic?

A million mirrors will work and there are no rules.. You need more INPUT.

We'd rather not click links..........thank you!

How is the vanity going to be configured? Drawers on both sides or drawers on one side? The vanities pictured below might be a little larger than the one you're going to have, but they show a variety of mirrors. IMO, sconces on the side provide the best quality light and in 46" you certainly have enough room to do that. But if you will have drawers only on one side that will present an issue for that configuration. Another option would be to have a mirror wall to wall and install sconces through the mirror. You can have a plain, large mirror framed by the builder with trim stock. If you leave it unframed it will have a cheap, builder-grade look.

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There will be three drawers on each side of the single rectangular sink. i would like to do a pivoted mirror ( simple black frame) . we are building an addition with the concept of aging in place. the pivot mirror would allow us to use it if we have to sit at the vanity.

the vanity is sherwin williams smokey azurite and will have black hardware on it. the counter top will be white.

i guess what im wondering is the shape of the mirror: oval or rectangle?

No pivot mirror will allow a view when seated, and a good make up mirror will do the same thing, where on a wall, or a set up on the counter top.

A round shape ( 30 or36 inch diameter ) will feel more current, is a pretty proportion with a rectangular sink and vanity size, but you haven't answered the lighting question. What and WHERE.

More important by far, than ANY mirror if you are setting about to age in place.

Missed that detail. Was considering a double/triple vanity light with glass dome positioned above the mirror. Unless there’s a practical reason to place otherwise
The vanity is tucked in a cubby.

https://www.crateandbarrel.com/dakota-black-3-light-wall-sconce-with-black-dome/s588325

This with glass dome