Grams to Ounces

The exact ounce, and where the nine decimals come from

Start with the pound, because the ounce is defined from it. The 1959 international yard and pound agreement fixed one pound at exactly 453.59237 grams, and a pound holds 16 ounces, so a single division gives the ounce:

1 oz = 453.59237 / 16 = 28.349523125 g

That is a definition rather than a measurement, which is why it carries nine decimal places. NIST SP 811, Appendix B.9 (Guide to the SI, 2008) prints the avoirdupois ounce as 2.834 952 E+01 grams and the pound as 4.535 924 E-01 kilograms. The BIPM SI Brochure, 9th edition (2019) covers the other end of the chain, since the gram is one thousandth of the SI kilogram.

Every result on this page comes out of that one number:

• ounces = grams / 28.349523125
• grams = ounces x 28.349523125
• 1 g = 0.0352739619 oz

Multiplying by 0.0352739619 is the same operation as dividing by 28.349523125, and the two agree to every digit a kitchen scale can show.

Two worked examples, step by step

Example one: 100 g of sugar. Divide by the ounce: 100 / 28.349523125 = 3.527396195 oz, which rounds to 3.53 oz. Check it backwards: 3.53 x 28.349523125 = 100.074 g, so rounding to two decimals moved the answer by 0.074 g.

Example two: a 750 g bag of flour written in pounds and ounces. Ounces first: 750 / 28.349523125 = 26.45547146 oz. A pound is 16 oz, so the whole pounds are 26.45547146 / 16 = 1.653467 lb, which is 1 lb plus 0.653467 lb. Turn the remainder back into ounces: 0.653467 x 16 = 10.45547 oz. The bag reads 1 lb 10.46 oz, and the two parts add back to 16 x 1 + 10.45547 = 26.45547 oz, the number we started with.

Going the other way takes multiplication. Four ounces of cheese is 4 x 28.349523125 = 113.3980925 g, and 2 oz is 56.69904625 g. A 12 oz bag of coffee beans is 12 x 28.349523125 = 340.1942775 g, the figure printed on bags sold in metric countries.

Both examples run on the converter above: grams in the first field, ounces in the second to run it backwards.

Grams to ounces table for cooking and shopping

A table beats a calculator when you are standing at the counter with flour on your hands. These values come from dividing each gram figure by 28.349523125, then rounding the fourth decimal place.

Doubling the grams doubles the ounces: 250 g to 500 g adds 8.8185 oz, and 500 g to 1000 g adds 17.6370 oz.

Troy ounces: the ounce gold is sold in

Gold, silver and platinum do not use the ounce above. Bullion trades in troy ounces, and one troy ounce is 31.1034768 g, the value NIST SP 811 Appendix B.9 lists as 3.110 348 E+01 grams. The troy system keeps 12 ounces to a pound and 480 grains to an ounce, so a troy pound is 12 x 31.1034768 = 373.2417216 g. That is lighter than the 453.59237 g avoirdupois pound even though it holds fewer, heavier ounces.

The gap between the two ounces is 9.7 percent: 31.1034768 / 28.349523125 = 1.097142857, so one troy ounce equals 1.097 avoirdupois ounces. A 50 g gold bar is 50 / 31.1034768 = 1.607537 ozt, not the 1.7637 oz a food scale would report. A 100 g bar is 3.215075 ozt. Reading the wrong column on a bullion quote overstates the metal by about a tenth, and at current gold prices that tenth is real money.

Grain weight explains where the two systems split. A grain is 0.06479891 g by definition, an avoirdupois ounce is 437.5 grains and a troy ounce is 480 grains. Same grain, different count, and the 42.5 grain gap is the 9.7 percent.

A scale that reads pounds and ounces

A US kitchen scale often reports pounds with a fraction, or pounds plus ounces, and the second format needs the remainder arithmetic from example two. 500 g is 17.636981 oz, and 17.636981 - 16 = 1.636981, so the display reads 1 lb 1.64 oz. 250 g is 8.81849 oz, under a pound, which reads 0 lb 8.82 oz. Two kilograms is 70.5479 oz, and 70.5479 - 64 = 6.5479, so 4 lb 6.55 oz.

A 340 g package is 11.9931 oz, which is 0.7496 lb, and 0.75 lb is 12 oz exactly. The label says 12 oz because the packer rounded at the ounce.

Metric labels, US labels and price per ounce

Importers print grams, US labels print ounces, and the two numbers rarely match to the digit. A jar marked 340 g is 340 / 28.349523125 = 11.9931 oz and sells as 12 oz. A 170 g bar is 5.9966 oz and sells as 6 oz. The 454 g package is 16.0141 oz, close enough to a pound that the label reads 16 oz, and it is 0.41 g over a true pound.

Unit price needs the same division, and this is where the conversion pays for itself. Coffee at $12 for 200 g costs 12 / (200 / 28.349523125) = 12 / 7.0548 = $1.70 per ounce. A 12 oz bag at $19.50 costs 19.50 / 12 = $1.63 per ounce, so the bag wins by about 8 cents an ounce. Put the two packages on the shelf and the bigger bag looks expensive; in price per ounce it is the cheaper one.

Every printed gram figure lands within half a gram of the exact value, smaller than any consumer scale can resolve.

Fluid ounces are volume, not weight

A fluid ounce measures space, and a gram measures mass, so no single factor connects them without the density of the liquid being poured. One US fluid ounce is 29.5735 mL, and a fluid ounce of water weighs 29.57 g at room temperature because a milliliter of water is about a gram. Honey is roughly 40 percent denser, so the same fluid ounce of honey weighs around 41 g.

That is the trap in recipes that mix the two systems. Eight ounces of chocolate on a US package means weight, 226.7962 g. Eight fluid ounces of cream means volume, 236.6 mL, which weighs about 242 g because cream is denser than water. The numbers look close enough to swap, and the cake tells you they were not.

When a recipe lists fluid ounces and your scale reads grams, use the grams to fluid ounces converter with the density of the ingredient rather than the 28.349523125 factor on this page.

Rounding, scale resolution and the mistakes that cost money

Three habits keep the numbers honest. First, decide the precision before you start: a scale that reads to 1 g cannot support four decimals, and 0.035 oz is the smallest step it can show. Second, round once at the end. Rounding 100 g to 3.5 oz and multiplying back gives 99.22 g, a drift of 0.78 g caused by two roundings instead of one.

Third, keep the ounce family straight. Mixing troy and avoirdupois on a gold sale changes 100 g from 3.215075 ozt to 3.527396 oz, a difference of 0.3123 ozt, which is about 9.7 g of metal.

The shortcut of multiplying by 0.0353 is accurate to 0.07 percent: 100 g reads 3.5300 oz against a true 3.5274 oz. That is fine for a shopping list and not fine for a lab notebook. The converter above prints four decimals on its own line and a two decimal line beside it, so you can take the precision the job allows and leave the rest.

Dividing by 0.0353 instead of multiplying turns 100 g into 2833 oz, an error of 800 times. Treating a kilogram as 32 oz rather than 35.2740 oz understates a 1 kg bag by 3.27 oz.