How many?

Micrometres

The micrometre or micrometer, also commonly known as a micron, is an SI derived unit of length equalling 1×10−6 metre; that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039 inch). The micrometre is often used to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles.

Metres

The metre, or meter, is the base unit of length in the International System of Units (SI). The SI unit symbol is m. The metre is currently defined as the length of the path travelled by light in a vacuum in 1/299,792,458 of a second. The current world record for running 100 metres is 9.58 seconds, set by Usain Bolt in 2009.