High 8-C would be enough to knock down a skyscraper especially if a bomb of that force is detonated from below. 8-A is if you punched a skyscraper and every wall, floor and ceiling got fragmented. Imagine Godzilla ramming through a 30-story building, smashing it to smitherenes - that is 8-A. High 8-C would be the bomb that can knock it down.
If I had to go by how the naming conventions correlate to their level of destruction i'd go with the following
9-B - Wall leve, can also be room level sometimes, mostly just enough to cause a wall to collapse.
9-A - Small Building level - true room level, enough to either cause pulverization or vfrag of walls, enough to shatter a small structure like a kiosk or a toilet building
8-C - Building level -
This and
this is the detonation of a 1 ton bomb. It can easily collapse a building that is 5+ floors tall.
High 8-C - Large Building level - enough to cause the collapse of a 30 floor+ building. I think everyone knows what skyscraper collapse one can think of here. We do not talk about it.
8-B - City-Block level - MOAB/FOAB level, can engulf around a hundred meters in diameter in flames, break most buildings in its way.
Here's a 50 ton explosion for reference.
8-A - Multi City-Block level - pre-nuclear level. Enough to obliterate every large building in the surroundings, heavy damage and possible destruction in the near mile or miles. While I do not like using this to explain something, the tragic Beirut explosion is estimated from 800 tons to over a kiloton, and it caused heavy damage and destroyed buildings for miles around.
Low 7-C - Small Town level - refer to above
7-C - Town level - Atom bomb level - Hiroshima and Nagasaki attacks annihilated the larger part of those cities, despite being detonated 500 meters in the air. Each bomb totalled a mile (despite being above ground) and caused fires further. A single one killed near 100 000 people.
High 7-C - Large Town level - nuke level. At this point it's basically city level just not quite. Idk why small city level exists tbh. Anyways, would pulverize everything within a few miles and cause widespread destruction furhter. Use Nuke Map to see just how bad it'd be.
Low 7-B - Small City level - pointless tier, is as strong as a megaton nuke. Just way stronger than above. Technically if you were to concentrate all that energy you could shatter a 600 meter mountain.
7-B - City level - Castle Bravo, Ivy Mike, Tsar Bomba - all of these are here. It is enough to vaporize a small island into nothingness. If you're standing on the ground and detonate tsar bomba in front of yourself, it would reach far beyond the horizon in its destruction, high enough destruction to bust buildings. Would incinerate a mountain to some extent
7-A - Mountain level - can cause the complete destruction of a mountain and more. The strongest erruptions like Krakatoa are on that level. Capable of not only shoving insurmountable amounts of dust into the air, enough to cover hundreds of kilometers, but also loud enough to be heard 4000+km away and that's for 200 megatons only. Would cause colossal tsunamis that could rip apart the sea floor.
High 7-A - Large Mountain level - gigaton tier. Tambora super volcano, Vesuvius, nigh-apocalyptic erruptions are on that level. Erruptions that can cause entire areas to become uninhabitable and threaten early civilization.
6-C - Island level - accurate. It would absolutely cause end of an island like Puerto Rico.
High 6-C - Large Island level - basically just small country level, it'd probably be enough to wipe out the island of Haiti of civilization and a good chunk of the mountains
Low 6-B - Small Country level - the teraton tier. Enough to cause an apocalyptic event, cause a massive earthquake across the entire globe, could wipe out a country like Spain or Germany in one shot.
6-B - Country level - the tier of the Chixulub meteor that nuked the dinosaurs. Could wipe out a country like Mexico or Japan with ease, would pulverize a notable hole in the earth and would cause an end of the world which even modern humans would struggle to survive in
High 6-B - Large Country level - enough to wipe out Brazil, Argentina, Kazakhstan, probably the US. Destruction great enough you could probably raze a third of the surface of the moon with it easily.
6-A - Continent level - Australia is doomed. Russia is mostly gone, the rest is on fire. There is a chunk gone from the earth.
High 6-A - anywhere from Russia getting wiped out in its entirety to the planet's surface being fully incinerated and molten down.
5-C - Moon level - Moon level, the moon gets broken apart and it cannot reform despite GBE
Low 5-B - Small planet level - Mercury gets shattered the same way
5-B - Planet level - The earth is either vaporized or its chunks are blasted away at such speed they cannot reform
I think the rest need no explanation since they're generally accurate with the level of variation of spacial bodies.
Ik I didn't need to do this but I was bored and did this for fun.