4500mm=4.5m=450cm.
1mm=(1/1000)m so divide mm by 1000 to get metres.
1mm=(1/10)cm so divide by 10 to get centimetres.
To divide by any power of ten, move the decimal point backwards one place for each zero. For example, to divide by 100, move the decimal point 2 places backwards. Whole numbers have an "invisible" decimal point after them, so "4500" is the same as "4500." or "4500.0".