How much roods in an acre?

There are four roods in an acre, according to The Oxford English Dictionary (OED) online, which gives among its definitions of "rood":

"7. a. A unit of land area equal to 40 square rods (a quarter of an acre, approx. 0.1012 hectare), but varying locally. Also: †a plot of land of this size (obs.). Cf. rod n.1 8b. Now chiefly hist."

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