Although they can be deeper, most graves now are 4-5 ft deep, so that the top of the burial vault is approximately 18-24 inches beneath the surface of the ground once covered. This makes for tidy, flat, mowing. When I was planning mine, I found out it's legal in most graveyards to come along later and bury an urn of ashes on top, from say a pet. That deeper depth to 6 feet was a result of the Black Death and a real fear of animals being be determined to dig them up.