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.

Centimetres

A centimetre, or centimeter, is a unit of length in the metric system, equal to one hundredth of a metre. For context, a piece of A4 paper is exactly 24 centimetres wide on its smallest side.