No way it was 5.4kt equivalent. Lebanese president confirmed there were 2,750 tons of ammonium nitrate being stored in the warehouse.

As it happens, that lines up extremely well with the yield calculations done by this redditor several hours ago. Ammonium nitrate has a relative effectiveness (RE is an index for how powerful the explosion is relative to the same mass of TNT) of 0.42, so 2,750 x 0.42 = 1105.5 tons, with that being the upper limit.

Keep in mind since it wasn't arranged for an optimal explosion, so actual yield is gonna be lower, which is why those 700-1000 ton numbers seem like a pretty good range.

At any rate it certainly wasn't 5.4kt, that'd be 30% larger than the largest conventional explosion in recorded history, which was set off intentionally. If we're talking accidental detonations, 5.4kt would be nearly twice the current largest recorded explosion, the Halifax Explosion, which was 2.9kt