What are Square Microns?
A square micron is the area of a square one micron (a millionth of a meter) on each side, which is 0.000000000001 square meters (10⁻¹² m²). It suits areas like the cross-section of a bacterium.
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.