[Soren]

Doesn't 4km diameter imply 4/3 2km ^ 3 = 10.66 km3 or about 11B cubic meters, or I am stuck in an alternate dimension again?

[Salgak]

We're both wrong: you forgot "pi", and I plugged in diameter instead of radius. . . it's 33.5 billion cubic meters, 263 trillion kg, 321 quintillion joules. Still a big bang. . .

[grania]

Doesn't 4km diameter imply 4/3 2km ^ 3 = 10.66 km3 or about 11B cubic meters, or I am stuck in an alternate dimension again?

The formula for the volume of a sphere is:

4/3(pi)r^3. So you were right to use the radius of 2, but I think you left out "pi". That is, you still need to multiply by 3.14.

That is, if you wanted to determine the volume. And if it's a sphere.