Until iMovie HD came out, it was easy to estimate how much disk space you needed to store a project: roughly 13 GB per hour of DV footage. HDV, however, is a different beast -- an HDV camcorder such as the Sony HDR-FX1 captures high-definition video and then compresses it in-camera using MPEG-2 compression (the same type used to encoded DVDs). In this compressed state, HDV doesn't take up more space on a MiniDV tape than DV footage. When you import it to your Mac, however, iMovie converts the video to Apple Intermediate Codec format, which takes up more hard disk space. But just how much? Unlike DV, it's not a fixed number.
HDV 1080i Apple Intermiediate Codec- per Bob Hudson
1080i 1440x1080 60i
10.7MB/sec 38GB per hour
depending upon the complexity of the video so it could well be that storage requirements could vary from 38GB to 50GB per hour.