A quick little background knowledge for you about print, mat, and frame sizes: some photography labs use the professional framing standard, and some use what the consumer framing standard.
Pro framing standard: "Hey, I have this 16x20 print. I want a 3-inch white mat, and a 1.5-inch black frame." You call it a 16x20 with a mat and frame.
Consumer places like Target, and some photography product labs: "Hey, I see this 16x20 frame. It has a mat and an opening for an 11x14 print." This really means you have a 16x20 mat, by the way. Which makes it even more confusing for overall dimensions.
So, what does Swift Galleries do? Swift Galleries uses the easier professional framing standard. When you see a 16x20 matted and framed print in Swift Galleries, it's a 16x20 print, with a mat and a frame. When you click the product, you'll see the mat width and the frame width. And those dimensions/widths you choose when you build (or load) a product.
Here are some helpful images for you to actually see what I mean...
When you load a product into Swift Galleries, or manually create a product in Swift Galleries, you'll see the mat color and width, and frame color and width, on the product description (bottom left above the three buttons), like this:
Here is what a framed and matted print (Millers' Blonde Maple framed print with the 2-inch white mat option) looks like in the wall art designer. Notice I've selected only the product on the left, and that product's details are on the left panel, showing a 20x30 print, a 2-inch white mat, and their 2-inch blonde maple frame:
The overall dimensions of the full gallery (when you click once to select the entire gallery), show dimensions edge-to-edge of the full gallery. So this does include the mat and frame for all products. This basically takes a measuring tape and says "this is how much wall is being covered by this gallery":
And here's an image that shows the math, all color-coordinated for you: