Fuel tank reserve capacity

Hi Kumud:
On my KLR 650 the reserve is 0.9 US gallons.
There's really not much point in worrying about "non usable" amount.
What I would recommend, especially if you're going to do any remote riding, is to strap a spare gallon (or 2) to your bike, then go for a ride. When you run out of gas, reset the trip meter to zero, turn on your reserve, and ride until you run out of gas again.
You will now know how far you can go on your reserve. That's the first important part.
Now put you spare gas into the tank and ride off to find a fuel station. Fill the tank, set the trip meter to zero, make sure the fuel selector is set to "ON", and go for a ride until you run out of gas again.
You will now know how far you can go on a full tank before you have to rely on the reserve.
If you use this system it won't matter what machine you have, and depending on your riding technique, the distances will vary.
Gotta love riding!
cheers.