Width is a length or distance. The unit of length is the meter.
It depends on the width of the desk. You could use centimeters or meters.
millimetres (or tenths of millimetres, if you have a micrometer)
A hair is about 50 µm (microns).
A centimeter is about the width of a finger.
there is no real metric unit. The SI unit is the second
measuring temperature the metric system of °C is used.