Consumer 8K usually means 7680 × 4320 pixels; consumer 4K usually means 3840 × 2160. That gives 8K four times the pixel count, but the visible improvement also depends on the source, screen size, viewing distance and compression.
Count the picture, not the label
A 4K frame contains about 8.3 million pixels, while an 8K frame contains about 33.2 million. These describe the picture grid rather than its sharpness in every situation. An out-of-focus camera image can still be encoded at either size, and neither number tells you how much fine detail the camera captured.
Follow the whole signal chain
Native 8K requires an 8K source, a compatible decoder, a suitable output connection and an 8K display. A player set to an 8K output may simply enlarge a lower-resolution stream. Look at the player’s media information as well as the television’s input information before deciding what is being delivered.
Decide from your seat
Compare the same scene from your normal sofa position. Small text, hair and distant buildings are more revealing than a colourful menu screen. Move closer only if you would normally watch there. For everyday viewing, stable motion, sensible compression and good contrast can matter more than increasing a resolution number.