Most cars don't show that. Here's the fuel gauge from my backup car since my other car is in the middle of repairs

Not only do you have to know the size of the tank, you also have to account for fuel tank math being different from regular math. The needle isn't linear. E.g in a lot of cars it doesn't start dropping until you're down at least like 5 liters. That's because people start whining about fuel consumption otherwise ("I just filled up and it's already dropping") and similarly the last half or quarter seems to be bigger in some cars. Middle bit is worth the least.

I don't think I've seen a car that actually shows the liters. Maybe once or twice. I've owned like 10 or 15 cars and driven many more.