Understanding Quarter Dome Mirror Sizes

When ordering any security mirror, a lot of unknown information is thrown at you. For example, what backing do I choose? Steel, plastic, hardboard, or even no backing. Next, what material should the mirror be made out of? Finally, dome mirror sizes. We have much information on this website about choosing the right mirror size.

Now and then, after a customer orders a quarter dome mirror, we get a call because the customer is concerned that the mirror they received may not be the right size…”I ordered a 32” quarter dome mirror, but it is much smaller after getting it. That’s because the size of the quarter dome mirror you ordered isn’t the size of the quarter dome mirror you received. What? That sounds crazy….I’ll explain below.

The size of a dome mirror is the diameter of the mirror. So, a 32” full dome mirror is 32” inches in diameter across the mirror (see diagram below). An 18” full dome mirror measures 18” in diameter…makes sense. The same holds with a half-dome mirror. A half-dome mirror is a full-dome mirror cut in half, but it still has the same size because it is the diameter of the full-dome mirror. A 32” half dome mirror is 32” wide, which is the diameter of a full dome mirror. A quarter dome mirror is where it starts getting a “bit” confusing.

The size of a quarter dome mirror is the radius of the entire dome mirror, not the diameter. So, a 32” quarter dome mirror will measure 16”. Check out the image below. If you notice the radius, that is the size of the quarter dome mirror. The radius of a 32” mirror is 16”, so if you order a 32” quarter dome mirror, each edge of the mirror (think of a pie slice) will measure 16”.

The example below is for a 26-inch and 36-inch quarter dome mirror. It shows the dimensions of each, respectively.