USA gallons are smaller than normal gallons....
its a 20 litre tank isn't it.... Since the free new fuel pump recall, mine runs out and stops with no fuel whilst still showing 11 miles to go. If yours has the trip computer... Wait till you're 20 miles to go, take a litre of petrol in a container and ride about within 5 miles of a fuel station (smoothly in a fairly upright boring manner, no mad acceleration or braking) and see what the range is at when it dies. Put the litre in the tank and ride like a cabbage to fill it up (and you should have 10 miles). Once at the petrol station fill it up and take off the amount you think you used. Then you know what range it stops at for future ref and what the size of the tank is when you fill it up..... Mine can easily get 2 litres more in on the side stand... when you patiently wait for it to settle before you keep pushing more in. And about 1 litre more after you brim it and keep trying on the centre stand.
But there's not much point, you can get 50 to 80 more mile out of a tank full by going slower. Ride 1000 miles across Europe at 60mph and miss every other fuel stop your mates need on their bikes doing 85mph and arrive at the same time with 200 quid more in your pocket and half your rear tyre left