The size of the pool you need for a family of 4 will depend on various factors, such as the size of your backyard, your budget, and how often you plan to use the pool. As a general guideline, a pool with a surface area of around 400-500 square feet is typically sufficient for a family of four.However, it’s important to keep in mind that the depth of the pool is also a factor to consider, as a deeper pool may require more water to fill and can be more expensive to maintain. In general, a pool with a depth of around 4-5 feet is a good option for families with children, as it provides enough depth for swimming and playing, while still being safe.It’s also important to consider other factors such as the shape of the pool, the amount of deck space you want, and any additional features you may want to include, such as a spa or water features.When planning the size of your pool, it’s a good idea to consult with a professional pool builder who can help you determine the best size and shape of pool for your specific needs and budget.