A kilogram is a unit used to measure the mass (some of you call it weight - depends on which planet you're on) of an object, like a bag of sugar weighs 1 kilogram (or 1kg). An adult can weigh 75kg. 1 kg is equal to 1000 grams (or 1000g).

A kilometre is a unit used to measure the length of really big things and distances, like the journey from Leicester to London, which is about 150 kilometres (or 150km). 1 km is equal to 1000 metres (or 1000m).