4.5 by 15 inches
The width is 2 1/2" by 12" in length which should be sufficient for most pieces of mail.
What we are showing here is for the outside of your home. If you need the inside, we do have that available without the flap for $139.95. What we have replaces an existing mailslot.
If you are installing a new mailslot where there has never been one before, in many cases, you will need a "sleeve" to go between the walls or the door (unless it is a solid core door). This is to prevent the mail from falling between the studs and the plaster or drywall. We do not carry the "sleeve" but this is something that you could probably get or have made locally. Don't cut into anything until you receive your items!