Center the mounting bracket or cleat on the back of the mirror frame and level with its top edge.
How to hang a heavy mirror on a plaster wall.
To hang mirror on a plaster wall use a toggle bolt outfitted with a picture hanging hook.
If you re hanging a heavy mirror on plaster without a stud your best bet is a hollow wall anchor such as a toggle bolt that expands and secures behind the plaster wall.
In addition to picking the right weight capacity the length of the hollow wall anchor is important because the bolt must extend beyond the wall so it can expand behind it.
Drill hole through plaster large enough to accept the toggle bolt.
Use a toggle bolt for heavier pictures or mirrors.
This hollow wall anchor will allow you to hang your frame anywhere without having to find a stud.
Thread machine screw through toggle bolt nut then pinch flat the wings on the toggle and push it through the hole in the wall.
Your mirror is too heavy for picture hooks alone but a wall anchor would likely do the trick to attach them to a wall made of drywall or plaster.
Interlocking brackets on the wall and the mirror provide secure and level hanging.
An easy to install french cleat hanging system is another mounting method to consider when learning about how to hang a heavy mirror.
Drill a hole and push in the bolt with toggle attached.