Good question Rab.
Lets take a 128 kbps stream as an example using the bandwidth calculator here : Internet Radio Bandwidth Calculator
128 kbps with 1 listeners (same as streaming to server) for 1 Hour (3600 seconds) = 0.05 GB = 56.25 MB
So 24 (hours) x 56.25 MB = 1350 MB or 1.32 GB...