It’s probably 43 pounds, but it was enchanted to only be picked up by the worthy; before it was enchanted, it was normal.

But I guess for the unworthy, it feels like 4.5 quadrillion pounds.

I mean I think it probably is 4.2 in actuality. It's just the enchantment makes it feel like far more to potentially infinite levels. Even for someone like Hulk who cannot physically lift it.

Like, the measurement is only for what it is exerting on the planet itself. Not the weight for lifting cause nobody can. And for Thor itself, he just has the godlike strength to lift something of this kind of mass.