An estate isn't just expensive property surrounded by a fence. Your estate is everything you own in your own name, and your share of anything you own with other people.
Money is property, too, as are stocks and bonds, a mutual fund account, or a life insurance policy.
But realistically, you need to know what it adds up to because the value determines whether any death taxes will be due, whether there's enough money to pay these taxes and other expenses, and whether there will be anything to leave your heirs. Since you own the property in your estate, it's your right to say what will happen to it. You might tell your spouse, your children, or your lawyer what you want to happen, but unless it's written down, there's no assurance your wishes will be respected. There are several ways to make clear what you want to happen to your estate. If you own your home, have invested money, and are in a pension plan, the value of your estate is apt to be greater than you think.