What are Square Inches?
A square inch is the area of a square one inch on each side, which is exactly 6.4516 square centimeters or 0.00064516 square meters.
What are Acres?
An acre is 43,560 square feet, which is about 4,047 square meters. It was originally the amount of land a yoke of oxen could plough in one day.
The United States and United Kingdom still measure land in acres, but most of the world uses hectares, which fit neatly into the metric system. One hectare is about 2.47 acres.