It was 50 KT though consider that the original design was to make the bomb 100 KT but Soviet Scientists were affraid about unknown affects a bomb of such a scale would have on earth Athmosphere so it was scaled down to ''only'' half of the original design.N.B Tsar bomba (as tested) was about 3000 times as powerful as the hiroshima bomb. Let us be thankful the cold war never went hot.