Oklahoma math

Larry Borsato points out that the Oklahoma City bomb was rather larger than the one ton (or tonne: one can't be sure, or surre) of ammonium nitrate claimed by RCMP Assistant Commissioner Mike McDonell at Saturday's press conference -- the basis of the "three times as big as Oklahoma City" meme. In fact, it was closer to 5000 lbs., or 2 to 2.5 tons (or tonnes). GlobalSecurity.org agrees:

By one estimate, the bomb used to attack the Alfred Murrah Federal Building in Oklahoma City on April 19, 1995 consisted of an ANFO [Ammonium Nitrate-Fuel Oil] explosive main charge of approximately 4,000 pounds, based on an estimate of the Velocities of Detonation [VOD] of approximately 13,000 fps. Other estimates claim that the 1995 explosion ... contained 4,800 pounds of ammonium nitrate and fuel oil. Later estimates suggested that the bomb had in excess of 6,200 pounds of various energetic materials, including explosives other than ANFO.

So the three tons/tonnes of AN involved in the current case would be enough for at most 1.5 Oklahoma Cities, not three. UPDATE: Angry has more. The apparent contradiction may be resolved if the Oklahoma bomb used a smaller ratio of ammonium nitrate to other ingredients. Apparently it can be as little as 36%. (UPPERDATE: But that does not appear to have been the case in Oklahoma City.)