The larger the greenhouse, the less temperature fluctuates, but that doesn't always mean bigger is better for your needs! About 6’ X 4’ or 6’ X 8’ is often a good size for a sizeable hobby greenhouse, allowing you to grow many plants. But the size that is right for you depends on your needs, including how much space you have. If you only have a small apartment terrace or balcony, even a small tabletop greenhouse will let you grow more plants than you could with no greenhouse at all!