The best way to figure out your fuel consumption is to ignore your tank size, and just compare how much fuel you actually use, and compare to your km each fill up. So fill up, reset your trip meter, ride it, and when you fill up next time, check your trip meter and see how much fuel you've used. It's all very good to look up the size of your tank, but we're not running it dry each time and we're not filling it to the brim each time either.
For comparison, my KZ750 LTD usually takes about 10 litres to fill from empty to full ('empty' being the low fuel light is on, 'full' meaning just below the bottom of the filler neck). That's for (what I believe) is actually a 14L tank. I'll get about 170km on a full tank, so around 6l/100km.