I have just about used one ball of each colour to get to the size of 27.5 inches. I had a tiny amount left of the red yarn but not enough to go round again. So if you want a big blanket, I would suggest you think about the completed size and how many rounds you are gonna get out of one ball per colour.

It crochets very quickly, what you see in the picture is about 3 hours of work. (I am a fast crocheter). You don’t need to worry about gauge because obviously it will grow very quick and the bigger size the hook, the quicker it grows or alternatively, use a smaller hook (no smaller than size 4) and it will become very thick and dense.

British crochet terms
No gauge given