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Gallons can't be converted to milligrams. Gallons measure volume, while milligrams measure mass.
1 gram = 1000 milligrams so 900 grams = 900*1000 = 900,000 mg. Simple!
Gallons are a measurement of volume, and grams are a measurement of mass (weight), so it would depend on what type of material you measuring.
900 micrograms is equal to 0.9 milligrams. To convert micrograms to milligrams, divide by 1000 since there are 1000 micrograms in a milligram.
There are 1000 micrograms in each milligram. You need to divide by 1000 here. 900/1000 is 0.9 milligrams.
Only if you have pure water in mind, then: 0.9 milliliters of pure water weigh 0.9 grams or 900 milligrams.
900,000,000 milligrams = 900,000 grams = 900 kilograms = 0.9 tonnes
About 14 gallons.
There are 1000 micrograms in one milligram. Therefore, 0.9 milligrams is equal to 0.9 x 1000 = 900 micrograms.
4 900 000 milligrams in 4900 grams (1000 milligram per gram).
13 gallons
14400 cups