Assuming that you mean winter squash exclusively. The larger the fruit the fewer a plant will bring to maturity. So if you are growing Dill's Atlantic Giant one per plant is all you want.Small ones like small acorns or mini-pumpkins like Jack-B-Little, you can have a dozen or more get to maturity. The plant is smarter than most of us, and if it sets to many,will abort the weakest until it reaches the amount it can bring to maturity.