There are 0.001 milligrams in a microgram. A microgram is 1/1000th of a milligram, which is, in turn, 1/1000th of a gram.
1 milligram = 1,000 micrograms
50 milligrams = 50000 micrograms
1 mg = 1 000 µg 250 µg = 0,25 mg
1 µg = 0.001 mg
2400 µg = 2.4 mg