Renting a car in the USA — how to know costs for the legal minimum liability insurance, before arriving for pickup?

Having rented many cars in the USA in many states and from many rental companies (as a US citizen), I can report that there is NO mandatory insurance required of the renter, only optional insurance. Car rental companies try to pressure customers to buy the insurance by saying that without the insurance you are responsible for the full value of the car. Don't worry. It is rare to have damage to a car, if you drive carefully. Further, many credit cards offer free auto insurance for car rentals. In my experience, in the past it was only the silver/gold/etc. cards that offered free rental car insurance, but now some regular credit cards offer this insurance also. (Check with your credit card customer service.) To take advantage of this rental car coverage (at no cost), all you need to do is use the credit card to pay for the rental and tell the clerk at the car rental desk that you are declining the insurance coverage from the rental company. You will have to initial in several places on the rental agreement, including one place indicating that you are declining the optional insurance. (You might be asked who your insurnce company is. I have no idea why rental companies ask this, but the answer is never verified.) This rental car insurance works worldwide. I have used it in various countries, not just in the USA. In short, using this approach allows you to pay the exact price you were quoted in your reservation, without any extra charge for insurance.

The issue would vary by state, but at least in California, all vehicle owners are required to have minimum liability insurance. Not just the drivers. What I think is happening is that no one can force Mr Hertz or Mr Avis to rent to people who don't have their own liability insurance, that will be responsible first in case of accident. (If you cause more damage than the amount of your own coverage, the victims will go after Hertz, too.)

If European insurance will not extend to the USA, there are a few companies that specialize in short-term arrangements that might be cheaper than the rental agencies.

First, the different prices you can get usually depend on your place of residence (i.e. not your driver license) and which website you book from. I wrote a detailed answer about the fact that car rental pricing is particularly complex. The liability insurance depends partially on your driver license.

Regarding liability insurance, the coverage provided by the rental company depends in which state you are renting your car.

For Hertz, there is a FAQ entry on the topic, and there are different levels of protection, the worst is in California if you have a US driver license, there is no protection. In other cases, you will get a minimal coverage (primary or secondary), usually what the state forces Hertz to have.

Upon signing the Rental Agreement, Hertz provides primary liability protection. However, such protection is generally no more than the minimum limits required by individual state law. See Financial Responsibility Limits by State.

The limits seems to be listed but Hertz claims it is not forced to respect these limits in all states, so this is more a maximum than a minimum amount:

Financial Responsibility Limits by State

The following chart lists the Automobile Financial Responsibility Limits of the various states. Hertz is not required to provide such minimum protection in all states.

So even if you do not see anything in your booking, there is a minimum coverage. If you are not satisfied, you can purchase the LIS (Liability Insurance Supplement) that covers way more ("USD 1,000,000.00 of combined bodily injury and/or property damage protection"). In Colorado and New York, you also get some coverage in case the driver causing the accident is not insured. In some other states, you may purchase such insurance (Uninsured Motorist Protection (UMP)) on top of the LIS. There is no consistent price across bookings, and you might not be able to book it in advance but most likely you can ask how much it is at the counter. In my memory, I vaguely remember that you could expect a price of 5 to 10 USD per day for such an insurance, but it really depends on every booking.

If you have a car, your car insurance may have a coverage for going abroad (most likely for many countries in Europe, at least, as you seem to live in Europe). If they do not cover rentals in the US in your current contract, they might offer such an option. You can still ask them.

If you want more details about insurances from Hertz, there is a long but very detailed notice.

In addition to Vince's great answer:

As a foreign driver, I never realized that having just the legal minimum liability insurance is completely insufficient. I was not aware, that this insurance covers basically nothing. Luckily nothing ever happened, but the thought still scares me.

Typically the minimum requirement very very low. In CA it is 15/30/5, which means up to 15k for death or injury of one person, up to 30k for multiple people, and 5k for damage to property.

That kind of money will be spent in a US emergency room in presumably less than a minute. If you have no money yourself means, should you injure or kill someone, he and his family will end up with a big hospital bill and probably loose their house, retirement, college education for kids, all that in addition to the accident.

Of course, you'll loose everything you have, too.

When I travel to the US, I now always rent a car through an international car rental agency and make sure that I have enough insurance. Typically you get around 1 million liability by default, and strangely you get this for the same price (or less) you would pay for the ridiculous 15/30/5 insurance that you get from the rental agency in the US.

I am completely puzzled that the US allows operating a car with effectively no insurance (in addition to 20% of the drivers having absolutely no insurance).