Well I tried an 8GB USB stick and ran out of room.
So I've answered by own question!
I wonder how long before a 16GB stick will be too small !!!
There used to be a day when a single floppy was enough for an OS install. Oh! how we have progressed(?) 
Please excuse my trip down memory lane and thanks to everyone for producing this RC so soon after the holidays.
 
-----Original message-----
> From:Bill Maidment <[log in to unmask]>
> Sent: Tuesday 10th January 2017 17:45
> To: [log in to unmask]
> Subject: SL7.3 RC Size
> 
> Hi
> I notice that the new iso is 7.8GB. Will it actually fit on an 8GB USB stick? Or do I have to buy a 16GB USB stick?
> 
> Cheers
> Bill Maidment
> 
>