Tablet Naming Conventions. Design lines and tablet sizes. Fire tablets have just three design lines, as shown above: Fire HD, Fire, and Fire HDX. Within each design line, there are different tablet sizes. The number in the tablet model, e.g., Fire HD 10 or Fire HD 8, refers to the tablet size (measured diagonally). Fire HD 10 is ten inches …

https://developer.amazon.com/docs/fire-tablets/ft-device-specifications.html