There are exactly 1,000,000 mg (milligrams) in 1 kg (kilograms). I know because kilo means 1000. Milligrams are smaller than normal grams, and there are 1000 milligrams in 1 gram. So kilo is 1000 and 1 gram is also 1000 mg. If you multiply 1000x1000 you get 1,000,000.