Tan as a unit of land area is a unit of multiples for tsubo (unit of land measurement; 1 tsubo is 3.31 square meters) which is the standard unit of area, and is now defined as 10 se (unit of area, 1 se is equal to 30 tsubo, about 99.174 square meters; 300 bu [歩; unit of land measurement; 1 bu is equal to 3.31 square meters]; 991.74 square meters).
土地の面積の単位の反、段は、面積の基本単位である坪（坪）の倍量単位であり、現在は10畝（300歩）と定義されている。