Convert milligrams to ounces

A milligram is one thousandth of a gram. The prefix milli in the SI always means a division by a thousand, so one gram holds 1,000 milligrams and one kilogram holds a million.

Milligrams are used for small masses: a vitamin dose, the caffeine in a drink, a stone in its setting, a weighed-out reagent.

An ounce describes masses tens of thousands of times larger. The avoirdupois ounce is one sixteenth of the international pound, which weighs exactly 0.45359237 kilograms[1], or 28,349.523125 milligrams[2].

That is why converting milligrams tends to give a number with several zeros after the decimal point. A dose printed on a label as a round number of milligrams drops to thousandths once it is expressed in ounces.

Alongside the avoirdupois ounce sits the troy ounce at 31,103.4768 milligrams[2]. You pick it in the card under the converter fields when you are weighing a precious metal.

Two hundred milligrams comes to 0.0070548 avoirdupois ounces. To convert milligrams to ounces, divide your value by 28,349.523125.

A metric carat weighs exactly 200 milligrams[3]. A one-carat stone is therefore also 0.0070548 avoirdupois ounces, and a half-carat stone 0.0035274 ounces.

A few other doses fall in the same range. Five hundred milligrams is 0.017637 ounces. One thousand milligrams, which is a gram exactly, gives 0.035274 ounces.

With the troy ounce the same doses give results 8.85 percent smaller, because that ounce is heavier.

Formula: ounces = milligrams ÷ 28,349.523125

The divisor is exact, because the international pound has a fixed mass and the ounce is one sixteenth of it. The answer carries seven decimal places so that a single milligram does not round down to zero.

For the troy ounce the divisor is 31,103.4768, so the same 200 milligrams gives 0.0064301 troy ounces.

The formula is a single operation: ounces = milligrams ÷ 28,349.523125.

Take the 500 milligrams printed on a supplement label. Dividing by 28,349.523125 gives 0.017637 avoirdupois ounces.

In your head it is easier to step through grams. Divide the milligrams by a thousand, then divide that result by 28.35. For 500 milligrams the first step gives 0.5 grams and the second about 0.0176 ounces.

In a spreadsheet a single function does the whole sum. In Excel, the formula =CONVERT(500,"mg","ozm") does the same sum[4]. The mass ounce carries the code ozm in this function, because oz on its own is not one of its mass units. Google Sheets uses the same name, and the mass ounce carries the same code ozm there[5].

The other direction is handled by the ounces to milligrams converter. To stay in metric units, move on to the milligrams to grams converter or the grams to ounces converter.

Gold, silver, platinum and palladium are weighed in troy ounces. It weighs 31,103.4768 milligrams, which is 2,753.95 milligrams more than an avoirdupois ounce[2].

The Krugerrand in the photograph below holds one troy ounce of gold, while the bars beside it are marked 1 KILO, which is 32.151 troy ounces. A bar's mass in grams is handled by the ounces to grams converter.

The apothecaries' ounce once used in prescriptions had the same mass as the troy ounce. Drug doses are stated in milligrams today. A mass given in pounds is handled by the pounds to ounces converter.

In the card under the converter fields you pick Troy (oz t), and the answer updates as soon as you do. For 31,103.4768 milligrams you then get exactly one ounce.