How do you find an area of a 12 mm and 10 mm square?

To find the area of a square, you multiply the length of one side by itself. However, in your question, you mention two different measurements (12 mm and 10 mm), which suggests you might be referring to a rectangle instead. For a rectangle, the area is calculated by multiplying the length (12 mm) by the width (10 mm), resulting in an area of 120 mm².