18 inch half dome mirror in warehouse

Understanding Dome Mirror Sizing

When ordering any security mirror, there’s a lot of unknown information 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 a lot of information on this website about choosing the right mirror size.

Every 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 after getting it, it is much smaller. That’s because the size of the quarter dome mirror you ordered isn’t actually 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 base of the mirror. An 18” full dome mirror measures 18” in diameter…makes sense. The same holds true with a half-dome mirror. A half-dome mirror is a full-dome mirror cut in half, but it still has the same diameter. A 32” half dome mirror is 32”, 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 full dome mirror, not the diameter. So, a 32” quarter dome mirror is going to measure 16”. Check out the image below.

dome mirror radius and diameter