The NASA said the explosion in the sky of Chelyabinsk was about 300 kilotons which is equivalent of 20 Hiroshimas
The diameter of asteroid was about 15 meters, its mass was 40 tons, and its speed was about 20 km/s (before entering the atmosphere). It is exploded at 30-50 kilometers above the ground.
It is considered as a biggest asteroid since Tunguska.