How small of a space can all the people of earth fit into?

You can fit an average human in a space 1 ft by 1 1/2 feet, without squeezing too much.

For 6.3 billion people, this makes an area a bit less than 340 square miles. That is a 18.4 miles by 18.4 miles square, i.e. not a very large area overall.

You don't need nearly that amount of space.

Your average human would fit in a 1.7m x 0.4m x 0.4 m box. They thus have a volume of (1.7x0.4x0.4) 0.272 cubic meters.

There are 6.3 billion people so the total volume of all people on the planet would be (0.272 x 6.3 billion) 171,360,000 cubic meters.

Thus...

Every human on Earth would fit into a cube about 1.2 km per side (cube root of 171,360,000).

Every human on Earth could stand in a field of about 31.8 km square kilometers (sqrt of (171,360,000/1.7)). That is about a third the area of Rhode Island.

it will fit in a peace of paper (any size), it's only 4 words right.

beside that there are so many ways you can do to fit them in a small spaces.