What is metric relation betion between Acre and Square Kilometers?  

1 KM^2 = 247.105381 acres

or

1 Acre = 0.00404685643 KM^2

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Here are some measurements for you dear friend ...

Square Inch
(sq in, in2) The area of a square measuring one inch on a side. There are 144 square inches in a square foot. 1 sq in = 6.45 sq centimeters.
Square Foot
(sq ft, ft2) The area of a square measuring one foot on a side. One sq foot = 144 sq inches = 929 sq centimeters.
Square Yard
(sq yd, yd2) The area of a square measuring one yard on a side. One sq yard = 9 sq feet = 0.836 sq meters.
Square Rod
(sq rd, rd2) The area of a square measuring one rod (16.5 feet) on a side. One sq rod = 272.5 sq feet = 25.29 sq meters. Uncommon unit.
Acre
(acre) The area of a square measuring approximately 209 feet on a side. 1 acre = 43,560 square feet = 4047 sq meters = 0.4047 hectares.
Quarter Section
(??) The area of a square measuring 0.5 mile (2,640 feet) on a side. Four quarter sections make up one section, which is equivalent to one square mile. One quarter section = 160 acres = 0.648 sq kilometers = 6.9 million sq feet.
Square Mile
(sq mi, mi2) The area of a square measuring one mile (5,280 feet) on a side. Also called a section. One sq mile = 640 acres = 2.59 sq kilometers = 27 million sq feet = 4 quarter sections.
Square Millimeter
(sq mm, mm2) The area of a square measuring one millimeter (0.001 meters) on a side. One sq mm = 0.01 sq centimeters = 0.00155 sq inches.
Square Centimeter
(sq cm, cm2) The area of a square measuring one centimeter (0.01 meters) on a side. One sq cm = 100 sq millimeters = 0.155 sq inches.
Square Meter
(sq m, m2) The area of a square measuring one meter on a side. One sq m = 10.764 sq feet = 1.196 sq yards = 0.0001 ares.
Are
(a) The area of a square measuring ten meters on a side. One are = 1076 sq feet = 100 sq meters = 0.01 hectares = 0.0247105 acres.
Hectare
(ha) The area of a square measuring 100 meters on a side. One hectare = 2.47 acres = 10,000 sq meters = 0.01 sq kilometers.
Square Kilometers
(sq km, km2) The area of a square measuring one kilometer on a side. One sq km = 247 acres = 100 hectares = 10,763,910 sq feet = 0.386 sq miles.