It's difficult to give an exact figure for the area of grasslands in square miles, as different sources use different definitions and classifications. However, here's a general idea:

* Rough estimate: Many sources state that grasslands cover about 20% of the Earth's land surface.

* Calculations: With the Earth's land surface estimated at approximately 57,308,738 square miles, 20% of that would be around 11,461,748 square miles.

Important Notes:

* Varying definitions: "Grasslands" can encompass various types of ecosystems, including savannas, steppes, prairies, and meadows. This makes defining the exact boundary of what constitutes a grassland challenging.

* Changing landscapes: Human activities like agriculture and urbanization have drastically altered natural grasslands over time, making accurate measurements difficult.

Therefore, while 11,461,748 square miles is a reasonable estimate, it's crucial to remember that the actual area of grasslands can vary depending on the criteria used.