Asteroid called 2016 QA2 back in August 2016 and asteroid AG13 this January 2017 miss our planet only by a few hundred miles. These objects were both in the same class, over 100 feet in diameter, but so small in the vastness of space that there’s almost nothing we can do to detect them. Even a rock over 100 feet in diameter can still cause a lot of damage even to the point of sustained infrastructure disruption depending on the impact zone. The blast of such meteors burning through our atmosphere would be about 30 times as powerful as the atomic bomb dropped at Hiroshima. The impact to the surface of the earth would depend on the decent angle of the object. Most asteroids have shallow angles of attack and would simply skip across the earth’s atmosphere then back out to space, but not all of them, and we are not always that lucky.