Convert ounces to milligrams

The avoirdupois ounce is one sixteenth of the international pound. That pound weighs exactly 0.45359237 kilograms[1], so dividing it by sixteen gives an ounce of exactly 28,349.523125 milligrams[2].

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

Milligrams are used for small masses: a vitamin dose on a supplement label, an active ingredient in a cosmetic, a stone in a ring. Ounces describe masses thousands of times larger: a bag of coffee, a stick of butter, a parcel.

Alongside the avoirdupois ounce sits the troy ounce, and that is the one precious metals trade in. It weighs 31,103.4768 milligrams[2], which is 9.71 percent more. You pick the kind of ounce in the card under the converter fields.

The avoirdupois ounce divides further. It holds 437.5 grains[2], and the grain still has its own narrow uses.

An avoirdupois ounce holds 28,349.523125 milligrams. To convert ounces to milligrams, multiply your value by that number.

Three values come out of this multiplier when you work with fractions of an ounce. Half an ounce is 14,174.76 milligrams. A quarter ounce gives 7,087.38 milligrams. Four ounces come to 113,398.09 milligrams.

Two further values describe parts of a pound. Eight ounces, or half a pound, is 226,796.185 milligrams. Sixteen ounces gives 453,592.37 milligrams, and that is the whole pound.

To read the same values in grams, move the decimal point three places to the left: four ounces is 113.39809 grams.

Formula: milligrams = ounces × 28,349.523125

The multiplier is an exact value, because it follows directly from the definition of the international pound. The converter shows the answer to three decimal places.

For the troy ounce the multiplier is 31,103.4768. One ounce of gold therefore comes to 31,103.4768 milligrams, which is 2,753.95 milligrams more than an avoirdupois ounce.

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

Take a mass of 3.4 ounces printed on an American package. Multiplying by 28,349.523125 gives 96,388.38 milligrams, or 96.39 grams.

In your head it is easier to split the multiplier in two. Multiply the ounces by 28, then by 0.35, and add the two results. For 3.4 ounces the first step gives 95.2 grams, the second 1.19 grams, and together 96.39 grams.

In a spreadsheet a single function does the whole sum. In Excel, the formula =CONVERT(3.4,"ozm","mg") does the same sum[3]. 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[4].

The other direction is handled by the milligrams to ounces converter. For a larger unit, move on to the ounces to grams converter or the pounds to ounces converter.

A fluid ounce is a measure of volume. A US customary fluid ounce holds exactly 29.5735295625 millilitres and an imperial fluid ounce exactly 28.4130625 millilitres[7].

Cosmetic and drink labels print this as fl oz. Volume is handled by the ounces to millilitres converter, which covers both of those values.

The mass of that same volume depends on density. Water at close to one gram per millilitre gives about 29,574 milligrams from a US fluid ounce, and an oil at 0.92 grams per millilitre about 27,208 milligrams.

This converter's field reads the number out of whatever you paste, so 8 fl oz is counted as eight ounces of mass. When your value describes volume, move to the ounces to millilitres converter and enter the same number there.