The average height of a Stormtrooper is ~1.8 meters
1.8 / 276 = .006 m/px
.006 x 1400 = 9.13043478261 m / 2 = 4.5652173913 m
Plugging this into a hemisphere calculator gives us 199270496 cm^3
We'll use fragmentation and vfrag:
199270496 x 8 = 1594163968 Joules, 0.38 Tons of TNT, Building level
199270496 x 69 = 13749664224 Joules, 3.28 Tons of TNT, Large Building level
This is a HUGE lowball as a good amount of rock is off-screen, but the AT-DP did blow through this like it was nothing.