Unit conversion is a multi-step process that involves multiplication or division by a numerical factor, selection of the correct number of significant digits, and rounding.
Length Conversion describe between the various different sizes by merely moving the decimal point the correct number of places. The basic metric units are meters (for length).
Area Conversion describes the total amount of space a 2 dimensional shape covers. The units used to describe an area are based on the length of a side of a square, the standard SI unit for area is the square meter.
Volume conversion a space any substance occupies or contains in a three dimensional space. While the Si unit for volume is the cubic meter, it is too big for common use and has been replaced with the liter (1 cubic decimeter) in everyday life.