About 109 Earths lined up side by side would approximately equal the Sun’s diameter.
The comparison comes from dividing the Sun’s diameter—about 1.39 million kilometres—by Earth’s diameter of roughly 12,742 kilometres. The result is approximately 109, making this a useful way to visualize the Sun’s enormous scale.
This is a diameter comparison, not a volume comparison. Although about 109 Earths fit across the Sun’s face, roughly 1.3 million Earths could fit inside the Sun by volume, because volume increases in three dimensions. The Sun itself contains about 99.86% of the Solar System’s planetary mass.
The figure is an approximation because both bodies are slightly oblate and measurements can vary by convention. The commonly quoted value of 109 refers to their mean diameters.