Hi ladylarch.

Let's see if my maths is up to this - if not, I'm sure someone will tell us!  It will depend on the recording mode. 

At the highest AVCHD setting of 50p the recording rate is 28 Mbps which equates to 3.5 MB/s, so it will take 287 seconds to use 1GB = 4.8 minutes per GB.

At a MP4 (1440 X 1080) the recording rate is 12 Mbps which equates to 1.5 MB/s, so it will take 667 seconds to use 1 GB = 11 minutes per GB.

So at the highest settings a 16GB MS would record about 76.8 minutes and a 32 GB MS twice that = 153.6 minutes.

At the MP4 recording rates this would be 176 minutes and  352 minutes respectively.

With the A77 you have a choice of recording rates - 3Mbps, 12Mbps, 17Mbps, 24Mbps & 28Mbps.

I hope that gives you a rough idea????  I'm sure it is in the manual somewhere but it won't download at the moment.