There are a ton of tutorials out there on how to frame a plate glass bathroom mirror using trim molding mitered on the corners, but I'm not fond of cutting miters!

Therefore this tutorial is how I framed my bathroom mirror without mitering.  In fact, if you had your measurements pre-determined, you could probably even do this without a saw!  Have your lumberyard/home improvement store cut the boards to length and you will be good to go.

So, without further ado.. the tutorial:

This is what my bathroom looked like when we moved in.  Since then I have replaced or spraypainted the brass fixtures,  refinished the cabinets, removed the sliding bath door, painted etc.  but I still had to deal with the wall-to-wall plate glass mirror.

 The first thing I did was remove it and took it to a glass shop to have it cut down.  I wanted it to end where the vanity ended, I didn't want a mirror behind me when I sat on the toilet.

 I then went to home depot and bought all the lumber I needed to frame the mirror.  All the cuts were square, nothing was mitred.  My mirror was about 3 feet tall by 5 feet wide after it was cut down.  I sketched out what I thought would look best and took my measurements with me to the home improvement store:

I laid the boards out on the floor of Home Depot to get an idea of whether or not the ratios would work (because the boards aren't cut to length,  I just compared one corner, where the boards come together to see what looked pleasing to me.)  This was the board layout I eventually settled on:

You can see that I decided against my original idea of 1x4s since 1x3s looked a little nicer to me.  To make it a little more finished looking I also decided to use a thin section of trim molding set on it's side (Originally I was picturing quarter round in my head, but I didn't like how it looked against the 1x2.)

 I also decided I wanted the bottom horizontal board to be wider than the top board because the top had the addition of crown molding that gave it the appearance of being wider.   After I selected the type of boards, I had them cut to length and laid out the final frame:

 

For my mirror (3 ft x 5 ft) my dimensions looked like this:

My cut list was:

(1) 1x2* cut to 69 inches

(1) 1x3* cut to 69 inches

(2)1-inch trim molding cut to 60 inches

(2) 1x3s* cut to 36 inches

(1) 75 inch long 3 inch crown molding

(I did decide to cut the ends of the crown at a 45 degree angle, and needed extra length. If you didn't mind the square end, like in the first sample photo, you could have it cut to 69 inches as well)

*Actual finished width of a 1x2/1x3 is 1.5 inches and 2.5 inches respectively

I took those boards home and painted them (make sure you paint the backs too!) the same color as my cabinetry (Martha Stewart's Burl) I nailed the trim molding and crown directly to the 1x2s and 1x3s making sure to center them exactly.  I then used Liquid Nails for mirrors to secure the 1x2 and 1x3 boards onto the mirror, abutting the vertical pieces to the trim molding making sure everything was square:

After the liquid nails dried, you could see the reflection of it in the mirror from certian angles (it dries white and showed up against the dark brown frame), so I then took black painters caulk and caulked the seams between the boards and the mirrors.  Because my boards were so dark, the black blended right in.  If you were going to leave your boards white you would use white caulk.

 Touch up the paint, and you are done!

I absolutely love how it came out. It makes the whole bathroom look so much more updated.

 And I also think it looks a lot more custom then a simple picture frame style border.  Plus.. NO MITERS!!

If you are interested in more details about the rest of the changes to this bathroom, HERE is the entire bathroom reveal and HERE is how I got rid of all the brass fixtures, updated the medicine cabinet etc. 

****UPDATE**** A few people have asked how the mirror is held to the wall.  I used these offset clips to attach the top and sides of the mirror to the wall, the bottom of the mirror sits directly on the backsplash: 

 

These clips are very low profile and the trim boards can lie right over the top of them (any small gap was masked with the caulk)  At the top of the mirror I actually put the boards below the clips and let a small portion of the mirror stick out since once the crown molding was up it covered any exposed mirror.  I didn't use any liquid nails on the back of the mirror and I didn't use those large plastic mirror clips.

Hope that helps!