Crochet blankets are a long-relationship project: a throw uses 1,500–3,000 yards of worsted-weight yarn and takes anywhere from a few weekends to a few months. The trade is that they're forgiving — small inconsistencies in tension blend into the texture, and most blanket patterns work in straightforward repeats you can pick up and put down.
For a baby blanket, a finished size of about 30×40 inches is standard. For a generous adult throw, aim for 50×60 inches or larger. Halve or double the foundation chain (in multiples of the stitch repeat) to scale any pattern up or down.