Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: What size opening will this need to mount in?
Document: There was no paper mounting template which there should be, so if your installing this from scratch, you'll need to measure carefully before cutting in to your boat. Also, the spring loaded door is cool, but when it opens it requires space up above the opening to roll up in to (about 1/2").
Have an 01 Crestliner fish hawk. This won't even begin to fit the factory opening (too wide).The Pyle's dimensions are more what I need.Don't make my mistake, measure your boat first.Quality seemed OK if it would have fit.
My experience with this unit was very good. Yes:  It was larger than the factory opening in my boat and required an enlargement of the opening. All well worth the effort, however in that the larger footprint is need to house what you cant see from the pictures:  This unit has a shelf for the radio that include double sided sticky tape.. This makes for a very sturdy installation base for the radio.
Have not installed because I don't really want to cut out the dash enough to mount it. Looks good.
Cut the hole to the correct size, drill in 4 screws (MUST be secure) and you can do it all from the front through the hole.
Easy to install and so far is doing great. very durable. Simple and it takes care of the need of keeping unecessary water away from radio.
Opening I had previous unit in had to be enlarged but am overall happy with fit on a outcome.
The unit was a little bigger than my old one. With the help of a jig saw I was able to widen the opening without to much work. It seems to be solid with the cover fitting snugly to protect my new stereo
This was replacing an old broken housing that no longer had its shield. To the point of one of the other reviews, it is bigger than my old one and required about a 1/4" bigger opening in both height and width. The holes also did not line up with the old one. I wasn't concerned about it, since I had no idea the brand of the old one, so couldn't match it up anyway.
dunno maybe 1/4 or 3/8" or a bit more? I mean, the hole you cut must have some open area at the top of it, behind the wall you are cutting into.
Answer: I cut a 3.25" x 8.25" hole.