Depends on the bitrate (32kbps, 64kbps, 128kbps, etc.).
Let's assume 64kbps,
64,000 (bits per second) x 10,800 secs = 691,200,000 total bits / 8 (bits per byte) = 86,400,000 total bytes = 86MB = 0.086GB
NOTE: One kb is actually 1024 bits, but I rounded to 1000 bits for simplicity/clarity sake.