1 GB = 1,024 MB (binary). Storage manufacturers sometimes use 1 GB = 1,000 MB (decimal), which is why a "500 GB" drive shows as ~465 GB on your computer.
Q: How big is a 4K movie file?
A 4K movie is typically 50–100 GB. A 1-hour 4K video at high quality is about 25–45 GB. A Full HD (1080p) movie is typically 4–15 GB.