It really does depend on how large you are going to make your cat cave, but I would estimate that this one probably weighed about 400 grams. To be on the safe side, I would purchase 500 grams of Botany Waste Yarn from World of Wool as the price is very reasonable. You won't get to choose your colors, as it will be a lucky dip. I find that it is wonderful for large or small projects. Just remember that it sometimes contains fibers which are not pure wool. These can be used to enhance the look of your cat cave but cannot be used on their own as they will not felt. Alternatively, you could use wool from a fleece to bring down the cost.