Scientists at Purdue University and Imperial College London have updated their popular
impact effects calculator first produced in 2004.
Users dial in details about the hypothetical impactor, like its diameter and density.
The web program then estimates the scale of the ensuing disaster, such as the size of the crater left behind.
It will also tell you how far away you need to be to avoid being buried by all the material thrown out by the blast, or set on fire.
http://www.purdue.edu/impactearth