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If there is one, it would be feet's. But, honestly, I can't think of an example for feet's.
20 Feet = 6.6666666667 Yard(s)
1 Yard(s) = 3 Feet
i think it is 0.333333333 yard
5,280 feet is exactly one mile.
A yard is equal to three feet, so one and a half feet would be half a yard.