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How to Calculate Grams & Milligrams

How to Calculate Grams & Milligrams
Syringes with milligram measurements Photo Credit Alison Roscoe/iStock/Getty Images

A gram (g) is the basic metric unit of weight. Calculating grams and milligrams (mg) is important for understanding medication doses, nutritional supplements, recipes, and similar calculations. In the US, where ounces (oz), the basic imperial unit of weight, are used, g and mg calculations must start by converting oz to g. One g contains 1,000 mg, and one oz contains 28.3495 g (usually rounded to 28, 28.3, etc., depending on the degree of precision you desire).

Grams to Milligrams

Step 1

Write, or enter into your calculator, the number of g which you want to convert to mg.

Step 2

Multiply the number of g by 1,000. Example: 2.25 g X 1,000 = 2,250 mg.

Step 3

Reverse the process to convert mg to g. Divide the number of milligrams by 1,000. Example: 1,250 mg divided by 1,000 = 1.25 g.

Grams and Milligrams from Ounces

Step 1

If you are given only oz but need to calculate g and mg, write, or enter into your calculator, the number of oz.

Step 2

Multiply the oz by 28 if you want an answer in g. Example 2.25 oz X 28 = 63 g.

Step 3

Use more decimal places for the value of g if you want a precise answer including mg. Example: 1.5 oz X 28.3495 = 42.5243 g, which can be read as 42 g and 524 mg.

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