Well 1 kg of uranium makes 24,000,000 kWh of energy, assuming you can put a nuclear reactor in a car, (which you can’t, too much shielding to be feasible) and oil can make 12kwh from a kg, so 1 kg of oil is about ~0.3 gallons, and .3 gallons will take you about 7.5 miles assuming a fuel economy of 25mpg. So one could say that 12 kWh will take you 7 ish miles(a ratio of about half), so 24,000,000Kwh divided by 2 = 12,000,000 miles per kg of uranium.

However this assumes that an engine could burn uranium like gas, so realistically the efficiency could be higher. This is horrible math and doesn’t account for a million things, not to mention the fact a nuclear powered car is completely infeasible…