Impact Diameter (meters)	Yield (Megatons)	Interval (Years)	Consequences
<50	<10	<1	Meteors in upper atmosphere, most don't reach surface
75	10-100	1000	Irons make crater like Meteor crater; stones produce air bursts like Tunguska; land impacts destroy area size of city
160	100-1000	5,000	Iron, stones hit the ground, comets produce airbursts, land impacts destroy area size of   large urban area (New York, Tokyo)
350	1000-10,000	15,000	Land impacts destroy area small state; ocean impact produces mild tsunamis
700	10,000 - 100,000	63,000	Land impacts destroy area size of moderate state (Virginia) ocean impact makes big Tsunamis
1700	100,000 - 1,000,000	250,000	Land Impact raises dust with global implication; destroys area size of large state or country (California, France)

from 'The Impact Hazard', by Morrison, Chapman and Slovic, published in Hazards due to Comets and Asteroids