Ounces to Grams Converter

The everyday ounce is the avoirdupois ounce: one-sixteenth of an avoirdupois pound. Since the pound has been defined as exactly 0.45359237 kilograms since the 1959 International Yard and Pound Agreement, the ounce is exactly 0.45359237 ÷ 16 = 0.028349523125 kg, or 28.349523125 grams. The value is exact by definition, so the conversion introduces no error of its own.

Going the other way, one gram is 0.035273962 ounces, and the far more useful anchor is that 100 grams is 3.5274 ounces — just over three and a half. Nutrition labels outside the United States are almost universally per 100 g, so that single anchor covers most label reading.

There is a second ounce that is not interchangeable. The troy ounce, used exclusively for precious metals, is 31.1034768 grams — about 10% heavier than the avoirdupois ounce. A troy pound contains only 12 troy ounces, not 16. Quoting a gold price 'per ounce' without specifying troy is a nine-percent error, which is why bullion markets always say troy.

A third source of confusion is the fluid ounce, which measures volume rather than weight. A US fluid ounce is 29.5735 milliliters. Eight fluid ounces of water happens to weigh about 236 grams, close enough to the 227 grams of eight weight-ounces that people conflate them — but that coincidence holds only for water, and fails badly for flour, oil, or honey.

American recipes measure by volume — cups and spoons — while European, Australian, and most professional recipes measure by weight. Weight wins for accuracy because volume depends on how the ingredient is packed. A cup of flour can weigh anywhere from 120 to 150 grams depending on whether it was scooped, spooned, or sifted, a swing of up to 25% that will visibly change a cake.

Standard baking weights are worth memorising: all-purpose flour is about 125 g per cup, granulated sugar 200 g, brown sugar (packed) 213 g, butter 227 g (which is exactly 8 oz, or two US sticks), and water or milk 240 g. Once you know these, converting a volume recipe to weight is a single multiplication per ingredient.

Ounce quantities in recipes are usually weight, not volume, when they refer to solids — 'a 14 oz can of tomatoes' is 397 grams. When they refer to liquids, they are almost always fluid ounces. If a recipe lists both 'oz' and 'fl oz', the distinction is deliberate and the two are not interchangeable.

Coffee is the clearest case for grams. A 1:16 brew ratio means 30 grams of coffee to 480 grams of water. Expressed in ounces that becomes 1.06 oz to 16.9 fl oz, which no one can measure repeatably on a kitchen scale. This is why every specialty coffee recipe in the world is written in grams regardless of country.

Postal rate bands are set in ounces in the United States and in grams almost everywhere else, and the boundaries do not line up. A US first-class letter tops out at 3.5 oz, which is 99.2 grams — just under the 100 g band used by many other postal systems. A package that is compliant in one system can be one band up in another.

Package weights on international shipping documents must be declared in the unit the carrier expects. Declaring 16 where the field expects kilograms rather than the pounds you intended overstates the shipment by a factor of 2.2, which can trigger a customs recalculation and a surcharge.

Food labelling rules in the United States require dual declaration: net weight in both ounces (or pounds) and grams. That is why a bag reads '12 oz (340 g)'. The gram figure is the rounded conversion of the ounce figure, not an independent measurement, so it will occasionally be a gram off from the exact factor.

Precious metals and pharmaceuticals sit at the precision end. Bullion is quoted in troy ounces, and pharmaceutical dosing is in milligrams — 1 ounce is 28,349.5 mg, a scale at which any rounding in the conversion factor would matter. Using the exact factor rather than a rounded 28.35 is the safe default in both fields.

A British bread recipe calls for 500 g strong flour, 350 g water, 10 g salt, and 7 g instant yeast. To follow it with American cup measures, convert to ounces first: 500 g = 17.64 oz, 350 g = 12.35 oz, 10 g = 0.35 oz, 7 g = 0.25 oz. Those are already awkward, which tells you something.

Translating to cups makes it worse. At 125 g per cup, 500 g of flour is exactly 4 cups — but only if the flour is spooned and levelled. Scooped directly from the bag it may be 3.3 cups, and the loaf will come out dry and dense. The 350 g of water is 1.48 cups, or roughly 1 cup plus 7.7 tablespoons.

The 10 g of salt is about 1.75 teaspoons of fine salt but nearly 3 teaspoons of coarse kosher salt, because the crystals occupy different volumes at the same mass. That single substitution is the most common reason a converted bread recipe tastes wrong.

The practical conclusion for anyone cooking across systems: buy a digital scale that toggles between grams and ounces, and convert the recipe once, permanently, into grams. A ten-dollar scale eliminates an entire class of error that no conversion table can fully solve.

Ounces to grams — 0.5 oz = 14.17 g · 1 oz = 28.35 g · 2 oz = 56.70 g · 4 oz = 113.40 g · 8 oz = 226.80 g · 12 oz = 340.19 g · 16 oz = 453.59 g · 32 oz = 907.18 g.

Grams to ounces — 10 g = 0.35 oz · 25 g = 0.88 oz · 50 g = 1.76 oz · 100 g = 3.53 oz · 250 g = 8.82 oz · 500 g = 17.64 oz · 750 g = 26.46 oz · 1,000 g = 35.27 oz.

Kitchen anchors — 1 cup flour ≈ 125 g · 1 cup sugar ≈ 200 g · 1 stick butter = 113 g (4 oz) · 1 cup water = 240 g · 1 tbsp = 15 g water · 1 tsp = 5 g water.

Related units — 1 lb = 16 oz = 453.592 g · 1 kg = 2.205 lb = 35.274 oz · 1 troy oz = 31.103 g · 1 stone = 14 lb = 6.35 kg.

Avoirdupois — from Old French for 'goods of weight' — became the English standard for general merchandise in the medieval wool trade. Its pound of 16 ounces displaced the older tower and troy pounds for everyday commerce, but troy survived for coinage and precious metals, and the apothecaries' system survived for medicine until the twentieth century.

The apothecaries' ounce was the same size as the troy ounce, 31.103 grams, and was divided into eight drams. Old pharmacy recipes, and some antique scales, use that system — so a nineteenth-century formulation converted with the avoirdupois factor comes out roughly 10% light.

The metric side is far simpler by design. The gram was originally defined as the mass of one cubic centimeter of water at its densest point, which is why a liter of water weighs a kilogram and a milliliter weighs a gram. That coupling of length, volume, and mass is the reason metric arithmetic works without conversion factors at all.

Modern definitions have moved on: the kilogram is now fixed by the Planck constant rather than by a platinum-iridium cylinder in Paris. Practically, nothing changed for cooking or shipping — the redefinition was designed to leave the kilogram's value untouched to well beyond any precision an ordinary scale can read.