1000 µg = 1 mg = 0.001 g

watermelon 500 g**
protein 3 g
protein quality 5 %
fat 1 g
linolenic acid 200 mg
carbs 41 g
total carotenes 4 mg
vitamin B1 220 µg
vitamin B2 250 µg
vitamin B3 750 µg
vitamin B5 8 mg
vitamin B6 350 µg
folic acid 25 µg
vitamin C 30 mg
vitamin K* 1 µg
calcium 50 mg
magnesium 14 mg
phosphorus 55 mg
chloride 42 mg
iron 2 mg
zinc 1 mg
potassium 1 g
copper 305 µg
nickel 70 µg
fluoride 55 µg
iodide 5 µg

* USDA Database
** Souci, Fachmann, Kraut;
Food Composition And Nutrition Tables
Medpharm Scientific Publishers Stuttgart