Is 897.60 square millimeters as big as a Polo field?
It's about 0.00000002 times as big as a Polo field
The size of a Polo field is about 50,167,641,600 square millimeters.
(for field polo) (United States Polo Association rules; unboarded side maximum)
An outdoor polo field must measure 274.32 m in length and 146.304 m to in width for a total playing area of up to 50,167,641,600 square millimeters. Polo traces its origins to an Iranian (then Persian) war game from the 5th Century, which was played with as many as 100 players per side.
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