Like the bombs physically or the explosions themselves?
I believe the bombs are similar to the size of maybe 3 or 4 men standing side by side. In FNV and F3 there are unexploded bombs which granted could just be reused assets that Obsidian did. But the mdoel reminds me of one that would be dropped from an bomber or airplane. But it think it depends on what launched the bombs themselves. Long distance missile silos from China to the U.S or from a nuclear sumbarine just off the coast.
We do see some of the missile silos in FNV in Lonesome road and see they are(Americans at least) they are hundreds of feet tall. But they mighr be intended for continental long launches.