You can't fit Earths *on* the diameter of the sun, because the diameter is a line, not a surface.

However, we can figure out how many Earths could be lined up across the sun's diameter. Here's how:

* Sun's diameter: 1.392 million kilometers

* Earth's diameter: 12,742 kilometers

Calculation:

1.392,000 km (sun) / 12,742 km (earth) = approximately 109 Earths

Therefore, about 109 Earths could fit across the diameter of the sun.