You can actually use any unit of measurement to measure something, but it makes sense to use the unit of measurement that:
An insect that is $8$8 mm long is easy to imagine, but if someone told you it was $0.000008$0.000008 km long, it would be tricky to imagine just how long it was. Here's a guide showing when to use which unit of measurement.
You can use any unit of measurement, but it makes sense to use the one that helps someone understand how long something is.
Choose the most appropriate unit of measure for the height of a tree.
Which of these is most appropriate to measure in metres?
Which unit is best to measure the mass of this truck?