All Things Are Relative
First keep in mind that most streaming services will adjust the stream based on available bandwidth. And the available bandwidth depends on more than your own connection to the internet. Outside factors may cause data congestion. And of course other devices on your own network may cause data congestion. But assuming a constant bit rate it is fairly easy to calculate how much data you will use in an hour. Just keep in mind that this figure is approximate. Also note that data rates use 1000 not 1024 for the calculations and use bits not bytes. A byte is 8 bits.
Playstation Vue recommends 10 Mbps (Megabits (not bytes) per second). Plus it recommends 5 Mpbs for each additional stream. Which seems to indicate to me that you really need 5 Mbps.
Netflix recommends 5 Mbps for HD quality. And it recommends 25 Mbps for 4K.
Amazon Prime Video recommends 3.5 Mbps for HD video. And you need 15 Mbps for 4K video. I assume Amazon compresses video quite a bit more than other providers.
VUDO recommends 4500 Kbps for 1080p. This is 4.5 Mbps. For 4K you need 11,000 Kbps. This is 11 Mbps.
For 1080p video most sites recommend 5 Mbps. To find out how much data that is in an hour use the formula below.
x 60 (60 seconds per minute)
= 300 Mb per minute
x 60 (60 minutes per hour)
= 18,000 Mb per hour (or 5 x 3600 (seconds per hour))
/ 1000 (1000 Mb in one Gb)
= 18 Gb per hour (Gigabits)
/ 8 (convert bits to bytes - 8 bits per byte)
= 2.25 GB per hour (Gigabytes per hour)
So one hour of 1080p video will use approximately 2.25 GB. A 4K stream needs up to 25 Mbps. So we can multiply our 5 Mbps stream by 5 to get 11.25 GB per hour.
If we stream 3 hours of 1080p video per night for 30 nights we will use 202.5 GB of data. This means we can avoid the 1 TB data caps for now. But, it is unrealistic to assume this will last long. Just converting to 4K will use more than the 1 TB per month. And it isn't uncommon for a family to have multiple streams. And every device today is connected to the internet and using a bit of data even when idle.
Here is a quick summary of the formula.
X Mbps x 3600 / 1000 / 8 = Y GB per hour
25 x 3600 / 1000 / 8 = 11.25