Twelve hides of land, at 120 acres per hide, comes to 1,440 acres. Randall points out that 144 is a recurring biblical number: 144 cubits in the wall of the holy city, and 144,000 redeemed of the earth, which he reads as the survivors of a catastrophe.
There are 43,560 square feet in an acre. Multiply 144 by 43,560, take the square root, and the calculator returns 7,920. That is the mean diameter of the Earth in miles.