I seldom drive without refueling to the point that the warning lights come on, but for various reasons I had the car out with the gas needle at about the 1/8th point when: (1) the yellow low fuel warning light on the dash lit up, (2) the info display between the speedo and the tach informed me of "low fuel," and (3) the NAV screen offered to find and display the nearest gas stations, which is quite handy.
I filled it up and noted the amount of gas needed, which was 14.5 gal. Since we all know that the RC fuel tank has a capacity of 17.5 gal, basic math (now probably high school math) tells us that there are about 3 gal left in the tank when the warnings alert you to a low gas situation. For most people that's about 50 miles, which is always nice to know.
Also, as the needle was conspicuously above the "E," I suspect that this gas gauge may be unusually accurate, and that allowing the needle to hit the "E" mark is not a good idea.
Happy motoring.

 

Nice to know the RC350 looks out for us when we forget to refuel in a timely manner. I think the reason the lights went off when you had 3 gallons was to protect the fuel injection system from sucking up any junk in the tank and fouling the injectors and or the fuel filter. Either way they really made it easy to let you know you're low on fuel.

Now if the car could have paid for the fuel that would have been even sweeter. LOL

 

Consistent with every other Lexus/Toyota I've owned or operated. About 2.5-3 Gallons left when the fuel light goes on.

 

The fuel remaining is about the same as in my previous Lexus cars, but in those cars the gauge needle is pretty much right on the "E" at the time. In my RC, in the one instance when I let the fuel get that low, the needle was quite a bit above the "E" and I was surprised to see the lights come one. In this car, perhaps, "E" means "E."