I just watched Season 9 Beachhead. Something I noticed:
Carter says the Mark IX bomb was "multigigaton. Visuals sort of show of this, though dialogue stated it would be 100 miles, visuals show something in great excess of this. Possibly two or three thousand miles.
Anyway, when Gerak arrives and till the shield covers the whole planet (3 different scenes total) I counted roughly 140 shots from the three Ha'Tak ships. Probably more off screen. Considering the rate of fire, let's round up to 200. Could be more than that though.
Carter also later stated that the Mk. IX bomb contributed to "nearly 70%" of the shield's power.
Ignoring the Prometheus's weapons for a minute, Garek's forces contributed 30%:
Multi-gigaton means many gigatons as in a handful. So let's not assume multi means 999 gigatons or even 99 gigatons.
1 Gigaton Mk. IX Bomb: 200 Ha'Tak shots: each Ha'tak shot is 2 megatons.
2 Gigaton Mk. IX Bomb: 200 Ha'Tak shots: each Ha'tak shot is 4 megatons
3 Gigaton Mk. IX Bomb: 200 Ha'Tak shots: each Ha'tak shot is 6 megatons
4 Gigaton Mk. IX Bomb: 200 Ha'Tak shots: each Ha'tak shot is 8 megatons
5 Gigaton Mk. IX Bomb: 200 Ha'Tak shots: each Ha'tak shot is 10 megatons
...and so forth. You get the idea. Anyway we do not know how truly powerful the Mk. IX bomb really is. It could be 2.2421 Gigatons for all we know and the Ha'Taks fired 500 shots and Prometheus's weapons could be extremely powerful like 50 megatons each (I counted six missiles) (Anyone doing the math: that is roughly 1.28 megatons per shot).
Hard to say though.