Lego bricks are made from acrylonitrile butadiene styrene (ABS), a common plastic. ABS has a density ~1.08 g/cm³. A standard 2x2 brick has a mass of 1.15 grams.
Generalizing for the sake of time, our attention spans, and my laziness, the Earth has a mean density of ~5.52 g/cm³. The mass of the Earth is 5.9721986x10
27 grams.
Doing simple math will tell you that you'd require somewhere in the neighbourhood of 5,193,216,173,913,043,478,260,869,566 2x2's (That's just over 5 octillion) to recreate the Earth just in terms of its mass.
But we adjust these numbers for Blockland's "real" scale (relative to Blockheads). A 2x2 brick measures as such.
So.
scale multiplier
conversion
There's the approximate mass of 2x2 in Blockland, 71.3 grams. Now let's refigure the mass equation with this in mind.
Ah. 83,761,551,192,145,862,552,594,670 (83 septillion) bricks, that's a bit more manageable.
Okay. So now we have the universe's largest toybox full of 83 septillion 2x2 Lego bricks. Now we have to put them into a sphere. Anyone who's built a sphere in Blockland probably knows that they're very approximate and very precise objects to build, but there is some math to it. I'll need a bit to work out a good way to calculate it though, so I guess there'll be a part 2 to this stupidity.
(I ended up not needing the densities because I don't care enough for precision, so enjoy the random trivia I guess)