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)
you times the width by the legnth of the shape
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.