Length
1 cm = 10 mm
1 m = 100 cm
1 km = 1000 m
Area
1 cm2 = 102 mm2 = 100 mm2
1 m2 = 1002 cm2 = 10 000 cm2
1 km2 = 10002 m2 = 1 000 000 m2
1 ha = 10 000 m2
Volume
1 cm3 = 103 mm3 = 1000 mm3
1 m3 = 1003 cm3 = 1 000 000 cm3
1 km3 = 10003 m3 = 1 000 000 000 m3
Capacity
These are the best ones to remember. The rest you can work out.
1 cm3 = 1 mL
1 m3 = 1 kL