4K, otherwise known as Ultra HD, is basically a measurement of how many pixels are on the screen, and anything 4K has a resolution of at least 3,840 x 2,160 pixels. A 3,840 x 2,160 resolution means that you have the width consists of 3,840 pixels and the height consists of 2,160 pixels. 1080p means a resolution of 1920x1080.
Higher resolution means more pixels to get you a clearer and better image. However, many people say that the video quality difference between 4K and 1080p to the naked eye is minimal. Actually, the visual differences become much more noticeable when the TV screen is larger (over 70 inches or larger) or when the watcher is further away from the television.
4K vs 1080p in Video Quality: 4K wins
4K vs 1080p in Video Source: 1080P wins
4K vs 1080p in Device Compatibility: 1080P wins