Why does my acrylic size/thickness vary?
Let's talk about cast acrylic and why it isn't always the same size or thickness. If you're new to acrylic, you may want to read up about the different ways acrylic sheets are manufactured HERE.
Cast acrylic, which is what the majority of acrylic sheets we carry are, is manufactured in molds. That means the parts that make the acrylic are poured into molds that are a set size and thickness. Because it is made in molds though, there is still some variance when the product sets. In fact, the industry standard is up to a 30% variance on thickness. This is a big reason why when you're using acrylic for projects that need to include stands and such, you need digital calipers to accurately gauge the thickness of every piece of acrylic you're cutting!
Because manufacturers vary, the actual mold length and width dimensions vary as well, especially when you are getting into specialty and decorative acrylic sheets. Standard mold sizes are 24" X 48", 48" X 72", and 48" X 96". Then you have to take into consideration the saw kerf and material that is cut off when your sheets are cut down.
We sometimes have questions about why some acrylic sheets are shorter than others, and this is why! We've standardized our options to an 18" width on our Glowforge sized acrylic sheets, so that is always a guarantee. More often than not though, you'll get closer to 19" or so on your acrylic sized sheets. We'd rather you expect less and get more than vice versa! But if you get a stack of acrylic and one sheet happens to be shorter than the rest, it is just a true 18 sheet!