[military] C4 most commonly comes in 1.25lb blocks. It's a pretty hefty boom, but it's not a lot when it comes to demolitions. It will straight up fucking wreck someone though.
For AP use though, the grenade comparison isn't right because grenades are filled with Composition B, and their killing power comes from the frag created by the casing not the explosive itself. The best Anti personnel comparison is the m18 Claymore which uses 1lb of C4 as its charge (again it's devastating effects are from frag as well)