1.2.4—The following prefixes and their symbols to indicate decimal submultiples or

Prefixes such as kilo (10³), milli (10⁻³), micro (10⁻⁶), nano (10⁻⁹) and pico (10⁻¹²) multiply the unit by a stated power of ten.

Convert the prefix before calculating, keep the exponent sign visible and distinguish a prefixed unit from a power of the base unit.

5.0 μm=5.0×10⁻⁶ m; 3.0 mm²=(3.0×10⁻³ m)²=9.0×10⁻⁶ m².

Squaring an area conversion squares the prefix factor too; converting 3 mm² as 3×10⁻³ m² is wrong.