The Best Way to Convert Grams to Milligrams (and Ounces to Grams)

Sometimes you need to do a little bit of math to convert grams and milligrams on a nutrition label.
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A gram (g) is the basic metric unit of weight. Converting grams and milligrams (mg) is important for understanding medication doses, nutritional supplements, certain recipes and similar calculations.


In the US, where ounces (oz), the basic imperial unit of weight, are used, gram and milligram calculations must start by converting ounces to grams.

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One gram contains 1,000 milligrams, and one ounce contains 28.3495 grams (usually rounded to 28, 28.3, etc., depending on the degree of precision you need).

Convert Grams to Milligrams

  1. Write, or enter into your calculator, the number of grams which you want to convert to milligrams.
  2. Multiply the number of grams by 1,000.
    • Example: 2.25 g X 1,000 = 2,250 mg
  3. Reverse the process to convert milligrams to grams: Divide the number of milligrams by 1,000.
    • Example: 1,250 mg / 1,000 = 1.25 g



Most medications and nutritional supplements are measured in metric units because it's the universal standard for scientific calculations. The metric system is also used for all everyday, household measurements and calculations throughout most non-English speaking nations.

Convert Ounces to Grams and Milligrams

  1. If you're only given ounces but need to calculate grams and/or milligrams, write, or enter into your calculator, the number of ounces.
  2. Multiply the ounces by 28 if you want an answer in grams.
    • Example: 2.25 oz X 28 = 63 g
  3. Use more decimal places for the value of grams if you want a more precise answer that also includes milligrams.
    • Example: 1.5 oz X 28.3495 = 42.5243 g


If you're making gram and milligram calculations to adjust or record medication dosages, please verify your calculations with a pharmacist, physician or other trained practitioner. Miscalculations can lead to significant under- or over-dosages.




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