The difference between full HD and 4K can be noticed without being too close to the TV. A 1080p TV has 1920 horizontal pixels and 1080 vertical pixels, while a 4K TV has 3840 horizontal pixels and 2160 vertical pixels. This means that a 4K TV has four times the amount of pixels than a 1080p TV, resulting in a more detailed and clearer image. The bigger the TV is and the closer you sit to it, the more likely you will be able to tell the difference between standard definition, 720p, 1080p, and even 4K. However, the difference may not be noticeable at larger distances or on smaller screens. Additionally, 4K TVs can make regular HD content look better through upscaling, which enhances the image to fill the extra pixels.