By the end of year 3 children should be confident with using comparative terms such as taller, shorter, longest etc. They should know that:
1 kilometre = 1000 metres
1 metre = 100 centimetres
1 kilogram = 1000 grams
1 litre = 1000 millilitres
They should also begin to recognise simple fractions and convert between units, such as that 3 and a half kilometres is 3500 metres.
Rulers should be used to a fair degree of accuracy.
This worksheet covers some aspects of this and would be a good assessment or homework sheet.