Part 1 Simon fucks up Dai-Gunzan with his drill. Let me first say that I have no reservations using the anime considering the anime is the original canon.
Spoiler:
According to his Wiki page, Simon's about 5ft (1.524m) tall, which sounds about right, I guess.
1.524m/202.9px=x/104.7px
x=0.78m
Spoiler:
.78m/4px=x/366.74px
x=71.5143m
Gurren Lagann is 71.5143m tall.
Spoiler:
71.5143m/18.7px=x/11.4px
x=43.6m
The length of the tip of Dai-Gunzan's blade to Enkidu is 43.6 meters.
71.5143m/18.7px=x/171px
x=654m
This will serve as the bare minimum height for the volume of rock fragmented, as Dai-Gunzan is completely engulfed by the cylinder excavated.
Spoiler:
43.6m/26.25px=x/651px
x=1081.28m
The diameter of the base of the volume of rock fragmented is 1081.28m.
Volume of a cylinder
v=(pi)r^2h
where r=540.64m and h=654m.
v=(pi)(292291.6096)(654)
v=600,542,807.42014350800614m^3
Violent fragmentation for rock is 120 j/cc, or 120,000,000 j/m^3
600,542,807.42014350800614(120,000,000)=72,065,136,890,417,220.9607368
or 17,223,981.09 tons of TNT
or about 17.2 megatons.
Is that right?
First time calc'ing DC, and I've had maybe 4 hours of sleep over 36 hours:distracted
Keep in mind that this is by episode 7 :gar
Spoiler:

According to his Wiki page, Simon's about 5ft (1.524m) tall, which sounds about right, I guess.
1.524m/202.9px=x/104.7px
x=0.78m
Spoiler:

.78m/4px=x/366.74px
x=71.5143m
Gurren Lagann is 71.5143m tall.
Spoiler:

71.5143m/18.7px=x/11.4px
x=43.6m
The length of the tip of Dai-Gunzan's blade to Enkidu is 43.6 meters.
71.5143m/18.7px=x/171px
x=654m
This will serve as the bare minimum height for the volume of rock fragmented, as Dai-Gunzan is completely engulfed by the cylinder excavated.
Spoiler:

43.6m/26.25px=x/651px
x=1081.28m
The diameter of the base of the volume of rock fragmented is 1081.28m.
Volume of a cylinder
v=(pi)r^2h
where r=540.64m and h=654m.
v=(pi)(292291.6096)(654)
v=600,542,807.42014350800614m^3
Violent fragmentation for rock is 120 j/cc, or 120,000,000 j/m^3
600,542,807.42014350800614(120,000,000)=72,065,136,890,417,220.9607368
or 17,223,981.09 tons of TNT
or about 17.2 megatons.
Is that right?

Keep in mind that this is by episode 7 :gar