For streaming in HD, 5Mbps is perfectly adequate for Netflix, etc. (Unless you're in a very remote rural area, it's almost impossible to subscribe to any service which doesn't offer at least that speed).
For streaming in 4K, you should probably be aiming for around 25Mbps.
The foregoing assumes that the movie connection to the internet is the only active one in the household at the time. It won't matter if, say, someone else in the house is simply doing a bit of web browsing, or using email, as the speeds I've quoted will still be adequate. However if you've got a house full of teenagers, where everyone wants to watch movies (or play online video games) simultaneously, you'll need higher speeds in order to cope with the additional traffic.