For the diameter of hair the best unit is micrometre.
I would imagine human hair would be measured in microns (micrometres or 10^-6 metres)
A hair is about 50 µm (microns).
get a ruler and measure it
By using a microscope.
A micrometre (millionths of a metre)
Millimeter
Identify the SI until you would use the measured the width of your classroom
You would use feet or yards to measure the width of a street.
yes
Multiply the height by the width Area = length x width or (height x width in this case)
how to measure the width of a hacksaw blade
It depends on what you are measuring the width of. Different units and different tools would be appropriate for a hair, a car or a galaxy.
METERS!!!The unit of measurement you would use to measure the width of your classroom is meters.
Centimetre.
Parsecs
a ruler
Millimetres
Identify the SI until you would use the measured the width of your classroom
15 m
a yard stick
meters
ruler
millimetres or even micrometres.