It's 12 wide. 55 1/2 long.
It is very useful. We keep toilet paper and bath products in it.
There is also a magazine rack on the side which has a back panel that opens for access to the tub.
Hope that helps!

thanks for the post and the response! I love this idea and cabinet too! So much better than a plain pony wall.

By the way Beaglesdoitbetter,do you recall the manufacturer or was it custom?

Custom. Dutchwood Kitchens in Myerstown PA. They did all the built-ins in our house and I truly love them. I highly recommend them if you are anywhere w/in 3-4 hours of the area. Affordable and a fantastic product.