You can't fit Earth *inside* the Sun, because the Sun is a giant ball of hot gas, and Earth is a solid planet.

However, you can ask how many Earths would fit *by volume* within the Sun.

Here's how to calculate that:

* Sun's volume: 1.41 x 10^18 km³

* Earth's volume: 1.08 x 10^12 km³

Divide the Sun's volume by the Earth's volume:

(1.41 x 10^18 km³) / (1.08 x 10^12 km³) = 1.3 x 10^6

Therefore, about 1.3 million Earths could fit inside the Sun by volume.