This question is incredibly vague considering there are multiple variables, particularly compression that affect this. Anyway here is what I found on a site about the Iphone video which records standard 1280x720p and 640x480p (I known standard NTSC is 720x480 but he can replace 640 with 720 and the formula will still work).

Based on:

```
Frame size K = ( [Pixel Width x Pixel Height x Bit Depth] / 8 ) / 1024
```

```
Where 8 represents an 8-bit byte, and 1024 equals the number of bytes per kilobytes.
To determine the file size of one second of uncompressed video, multiply the image size by the number of frames per second (fps).
To determine how compression affects file size, divide the file size by the compression ratio.
```

480P would be:

```
( [640 x 480 x 24] / 8 ) / 1024 = 900 KB / frame
900KB/frame x 30 frames/sec = 27000 KB/sec
27000 KB/sec / 40 compression ratio = 675 KB/sec compressed
675 KB/sec * 250 min * 60 s / min * 1 MB / 1024 KB * 1GB / 1024 MB = 9.66 GB (39 MB / min)
```

720P would be:

```
( [1280 x 720 x 24] / 8 ) / 1024 = 2700 KB / frame
```

```
2700 KB/frame x 30 frames/sec = 81000 KB/sec
81000 KB/sec / 40 compression ratio = 2025 KB/s compressed
2025 KB/sec compressed * 250 min * 60 s / min * 1 MB / 1024 KB * 1GB / 1024 MB = 28.97 GB (118 MB / min)
If a higher 60:1 compression ratio is used by the more powerfull iPhone 4: 79 MB / min
```

Source I'll post more if I find anything on 1080P or you can just use the above formula it seems pretty solid.