This pattern is written in US terms and is worked in rounds. The initial design is a 13 round square, a customized sized throw can be made using multiple squares or repeating the last 4 rounds. Your finished blanket will depend on your choice of yarn and hook and your tension. The 18inch sizing is based on medium #4 yarn and a 7.0mm hook.
Great for using up leftover yarn as the instructions allow for a colour change every round if you wish.