When we have the prefix (before a word) kilo it means 1000
1 kilogram = 1000 grams
1 kilometre = 1000 metres
When we have the prefix (before a word) milli it means 1⁄1000
1000 millimetres = 1 metre
1000 millilitres = 1 litre
When we have the prefix centi it means 1⁄100
100 centimetres = 1 metre