mm
cm
m
km
100

10cm is...

100mm

100

Bigger or smaller - is 20 cm > 0.5 metre

No. 0.5m = 50cm
100

60cm is...

0.6km

100

measure a road trip

Yes, it is an appropriate unit of measurement

it's the biggest unit

200

3m is...

3000mm

200

0.93m is...

93cm

200

3380mm is...

3.38m

200

200m is...

0.2km

300

Measuring a car

Not appropriate unit of measure.

The unit is far too small

300

measuring a pencil

Yes, this is an appropriate unit of measurement

Easier the mm and still accurate.
300

measure a pathway

yes, this is an appropriate unit of measurement. 

cm and mm would be too small

300

4688cm is...

0.04688km

400

Hair or nail growth

Yes, this is an appropriate unit of measurement.

They grow very slowly and will be most accurate.

400

0.00075km is...

75cm

400

How do i convert from cm to m and back again?

cm/100 = m

m x 100 = cm

400

mm to km and reverse

mm/1,000,000 = km

km x 1,000,000 = mm