If you weren't concerned with preserving life, you could take the current population of Earth, multiply by the average weight of a human (69kg according to Wolf

If you weren't concerned with preserving life, you could take the current population of Earth, multiply by the average weight of a human (69kg according to Wolfram Alpha's sources), assume that we have the same density as water, and find that we could all fit in a 0.5km³ box.