SO like PhiliFrisbie mentioned, bitrate is how its determined and there are different Freeview settings on different devices. Does yours have the SD or HD version of freeview? With freeview HD PlayTV, your looking at 2GB for a half hour or 4GB for 1 hour so about 4 hours of recording time as a worst case scenario guess (Worst case scenario, Or best quality i should say. If you choose a lesser quality, you will get much more recording hours stored). IF you have a Standard Definition you will get more than that. Get us some more information if you want to know the exact numbers otherwise there is no theoretical number that can beat the real thing! Go and just record to your hearts desire and see how large half hour and 1 hour shows are in the various modes, compare the end quality vs file size and you can then determine which is the best for you or you could even record your favorite shows at the highest setting while other shows are at less quality so as to pack more into whatever limited space you have.