[dgacmu]

How do you calculate this? Starship has a propellant capacity of 1200 metric tons - 1.2 kilotons. Super heavy booster has 3400 tons, total of 4.6 kilotons, per wikipedia [1]. By weight, you need about a 4:1 ratio of O2:Methane for complete combustion (Starship is rumored to carry 22% methane). Which means you're getting about 0.92 kilotons of methane completely combusted. At 50-55MJ/kg, that gives you - roughly - 50 thousand gigajoules. A ton of TNT is 4.184 thousand gigajoules[2], which means that Starship+Super Heavy carries the energy-equivalent of about 12 kilotons of TNT [3][4].

[1] https://en.wikipedia.org/wiki/SpaceX_Starship

[2] https://en.wikipedia.org/wiki/TNT_equivalent

[3] It can't explode all at once unless pre-mixed in perfect proportion, of course. What you'd really expect is an awfully big fireball + fire but not the same massive force all at once of a nuclear detonation.

[4] Or 50 terajoules (the ship) and .184 terajoules (TNT), which come out to the same thing, but I find gigajoules both more intuitive and more a more fun BTTF reference.