1 Ounce to Grams

One ounce is 28.349523125 grams, exactly

The ounce most of the world means when it weighs food, parcels or a baby is the avoirdupois ounce, and it is not a measured quantity. It is a legal one, fixed by arithmetic.

On July 1, 1959, the National Bureau of Standards put the international pound at exactly 0.45359237 kg, as recorded in the Federal Register announcement of that year. Sixteen ounces make a pound, so 0.45359237 / 16 = 0.028349523125 kg, or 28.349523125 g. No measurement enters the chain. The same announcement fixed the grain at 0.06479891 g, and 437.5 grains make one ounce.

Turn it around and one gram is 1 / 28.349523125 = 0.0352739619 oz. A 100 g chocolate bar is 3.5273962 oz, and a 1 kg bag of rice is 35.2739619 oz.

NIST SP 811, Appendix B.8 (2008 edition, updated in 2025) prints the ounce as 28.349 52 g for daily work, and the BIPM SI Brochure (9th edition, 2019) is the reference for the gram itself. Keep the nine decimals when you are converting a batch or a price. Round at the end, not at the start.

Eight ounces, one cup of butter, two sticks

Butter is where the ounce earns its keep in a US kitchen, because a stick is 4 oz and a cup is two sticks. Eight ounces is 8 x 28.349523125 = 226.796185 g, and that is the weight of one cup of butter on every US stick wrapper.

A single stick is 113.3980925 g. Cut it into tablespoons and each of the 8 pieces is 14.1747616 g, since 113.3980925 / 8 = 14.1747616. A recipe that calls for 6 tablespoons of butter wants 85.0485694 g, which is one stick plus two tablespoons.

European butter usually comes in a 250 g block, not a half pound. A 250 g block is 8.8184905 oz, so it is 1.18 oz more than two US sticks, and a recipe built around two sticks will taste slightly richer with the whole block. Weigh it if the dough is tight.

A kilogram in ounces, and the pounds plus ounces reading

Metric labels are the common case in the other direction. One kilogram is 1000 / 28.349523125 = 35.2739619 oz. On a scale that reads pounds and ounces, that is 2 lb 3.27 oz, because 2 lb is 907.18474 g and the remaining 92.81526 g is 3.2740 oz.

Half a kilogram is 17.6370 oz, which is 1 lb 1.6370 oz. A 250 g pack is 8.8185 oz, just over half a pound. A 100 g serving is 3.5274 oz, close to a quarter pound minus a nibble.

Postal and shipping rates still quote ounces in the US, so a 1 kg parcel is billed as 36 oz once you round up, not 35.27. That rounding rule costs money on light, bulky items, and it is worth knowing before you print a label.

Familiar sizes help. A 750 g bag is 26.4555 oz, or 1 lb 10.46 oz, which is why a European 750 g pack feels like a 1.65 lb bag. A 340 g jar is 11.9932 oz, close enough to 12 that the two labels get used interchangeably.

Troy ounces: 31.1034768 grams and the 9.7 percent gap

Gold, silver and platinum are sold by the troy ounce, and it is heavier than the food ounce. One troy ounce is 480 grains, and at 0.06479891 g per grain that is 31.1034768 g. The avoirdupois ounce is 437.5 grains, so the troy ounce carries 42.5 more grains and 9.7 percent more mass.

In ounce terms, one troy ounce is 31.1034768 / 28.349523125 = 1.0971428571 avoirdupois ounces. A 1 kg bar is 32.1507466 troy ounces. Eight troy ounces, a common coin and bar size, is 248.8278144 g.

Prices follow the troy ounce, so the per gram figure is the one to compare with a metric quote. At $2,400 per troy ounce, gold is 2400 / 31.1034768 = $77.16 per gram. A dealer quoting $80 per gram is charging a premium of about 3.7 percent over the spot price, before any fabrication charge.

There is no such thing as a troy pound in retail metals, even though the unit exists at 12 troy ounces, or 373.2417216 g. If a listing says pound, ask which one.

Kitchen equivalents: cups, tablespoons and grams

A cup is a volume, so the gram weight depends on what fills it. USDA FoodData Central lists a US cup of all-purpose flour at 125 g, granulated sugar at 200 g and water at 236.59 g. Those three numbers cover most of the conversions a home cook needs.

One ounce of flour is 28.349523125 / 125 = 0.2268 cup, a shade under a quarter cup. One ounce of sugar is 0.1417 cup, or 2.27 tablespoons, since a tablespoon of sugar is 12.5 g. One ounce of butter is 2 tablespoons exactly.

The tablespoon figures come from dividing the cup weight by 16: flour 125 / 16 = 7.8125 g, sugar 200 / 16 = 12.5 g, butter 226.796185 / 16 = 14.1747616 g, water 236.5882365 / 16 = 14.7867648 g. A digital scale set to grams beats a set of cups for anything that clumps.

Fluid ounces are volume, not weight

The fluid ounce is a volume unit and the ounce is a mass unit. They share a name and nothing else. One US fluid ounce is 29.5735295625 mL, which is exactly 2 tablespoons, and a 12 fl oz can holds 354.8823548 mL.

Water is the one case where the two line up closely: at 1 g per mL, 1 fl oz of water weighs 29.5735295625 g, and 12 fl oz weighs 354.8823548 g. That is why a 16.9 fl oz water bottle is labeled 500 mL and weighs about 500 g.

For anything else you need a density. Honey at about 1.42 g per mL puts 12 fl oz at 504 g. Flour scooped into a cup is 125 g over 236.5882365 mL, or 0.528 g per mL, so 12 fl oz of flour is only about 187 g. Same volume, less than half the mass of the honey.

A US pint is 16 fl oz, 473.176473 mL, and a quart is 32 fl oz, 946.352946 mL. A 16.9 fl oz bottle is 500 mL by design: 500 / 29.5735295625 = 16.9070 fl oz, rounded down to 16.9 on the label.

This is the mistake behind dense cakes and dry cookies: a recipe written in fluid ounces assumes water, and the ingredient is not water.

Price per ounce from a metric label

Unit price tags in the US use ounces, and imports use grams. To compare, divide the price by the grams, then multiply by 28.349523125.

A $4.99 item sold in a 100 g pack is 0.0499 per gram, which is 4.99 / 100 x 28.349523125 = $1.4146 per ounce, or $22.63 per pound. The same product at $12 for 500 g is 0.024 per gram, or $0.6804 per ounce, less than half the unit price.

Cheese, coffee and spices all play this game. A 170 g wedge at $2.49 is $0.4152 per ounce. A 454 g bag at $8.99 is $0.5614 per ounce, which looks cheaper per bag but costs more per ounce than the small wedge.

Rounding, scale resolution and the 0.1 ounce line

Kitchen scales read in 1 g steps, postal scales in 0.1 oz steps. One gram is 0.0352739619 oz, so a 1 g scale can show a 0.035 oz change. A 0.1 oz step is 2.8349523 g, which is coarse enough to hide a whole tablespoon of flour.

Rounded factors are fine for a shopping list and risky for a formula. Using 28.35 g instead of 28.349523125 g loses 0.000476875 g per ounce, which is 0.0076 g over a pound. Using 28 g loses 0.349523125 g per ounce, or 5.59 g over a pound, and that one shows up in baking.

Package labels add their own rounding. A 453 g bag is 15.9790 oz, not 16, and a 454 g bag is 16.0143 oz. Neither is a full pound by the legal definition, though both pass the net weight rules that allow a small average shortfall.

The practical rule: convert with the full factor, then round the final number to the precision of your scale. Do not round the factor first.