Convert g to oz

Grams are the unit of recipes and postage outside the United States, and the unit nutrition labels use nearly everywhere.

An ounce is a sixteenth of a pound. It is not the fluid ounce, which measures volume, and the two are only loosely related — a fluid ounce of water weighs about an ounce, which is where the name came from and where the confusion starts.

The factor is 0.035274, and almost nobody carries that around. Rounded to 0.035 it is off by 0.78 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 g.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

The ounce has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 28.3495231 g to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is not the whole of it, though: this page stops at nine significant digits and the ratio carries on past them.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

The ounce this page converts is the avoirdupois ounce, a sixteenth of a pound, 28.349523125 g exactly. The fluid ounce is a volume — 29.57 ml in the US, 28.41 ml in the UK — and appears in the same recipes, sometimes in the same line. The troy ounce, 31.1034768 g, prices gold and silver and turns up in a kitchen only by accident, but it is the reason a gram-to-ounce answer copied from a bullion site will not match this one.

The names collided because an imperial fluid ounce of water was defined to weigh about an ounce, which made the two interchangeable for the one substance and for nothing else. A US recipe asking for 8 oz of chocolate means a mass and one asking for 8 oz of milk means a cup — and the only reliable tell is what is being measured, not how it is written.

The deeper problem behind grams-to-ounces is that US home cooking measures by volume. Flour, sugar and butter are cups and sticks and tablespoons, so a metric recipe converted honestly to American units often does not produce ounces at all — it produces cups, and the conversion from 500 g of flour to cups depends on how the flour was packed into them.

That is why weight-based American recipes, when they exist, are usually from bakers, and why they are better sources to convert against. A gram figure has a single unambiguous ounce equivalent and no unambiguous cup equivalent: 125 g of flour is 4.41 oz always, and is somewhere between three-quarters and a full cup depending on whose hand scooped it.

Rounding the ounce to 28 g is short by 1.2 per cent, which disappears in a single ingredient and does not disappear across a whole recipe scaled up. A batch calling for 1,000 g of flour converted at 28 comes out at 35.7 oz against 35.27 exactly — a difference of about twelve grams of flour, which is nothing, until the same error runs through the water and the salt in the same proportion and the hydration ends up where it started.

The practical rule is that proportional errors cancel and absolute ones do not. If every ingredient is converted with the same slightly wrong factor, the recipe still works, because a recipe is a set of ratios. What breaks it is converting the flour precisely and the yeast approximately, or rounding a 7 g sachet to a quarter ounce, where a fifth of a gram is a real fraction of the ingredient.

US ingredient packaging is built on the sixteenths of a pound rather than on round ounces: 4 oz, 8 oz, 12 oz, 16 oz. Those are 113.4 g, 226.8 g, 340.2 g and 453.6 g, and none of them is a round metric number — which is why a European recipe never asks for 340 g of anything and an American one asks for twelve ounces of it constantly.

Converting in that direction is often better done by the packet than by the number. A recipe wanting 200 g of chocolate against an 8 oz bar is asking for a little over seven-eighths of it, and cutting a bar by eye to 88 per cent is more accurate than most scales are in ounce mode. Where the metric figure is close to a packet, the packet is usually what the original recipe assumed.

Domestic kitchen scales weigh to the nearest gram and display ounces to a tenth. A tenth of an ounce is 2.835 g, so the ounce display throws away most of the resolution the instrument has — a reading of 1.4 oz covers everything from about 38 g to 41 g, and the scale knew which.

This matters for the ingredients where small quantities carry the recipe: salt, yeast, baking powder, spice. Weigh those in grams regardless of what the rest of the conversion is doing, and reserve the ounce display for the bulk ingredients where a couple of grams either way is genuinely invisible. Switching units mid-recipe is allowed; a scale that can do both is why.

US packaging law requires the net contents in both customary and metric units, so an American packet carries both numbers already — "8 oz (227 g)" — and the metric figure is the rounded one. That rounding is where a conversion and a label disagree: 8 oz is 226.796 g and the packet says 227, which is right and is not what the field above prints.

The direction of the rounding is worth knowing when the pack is the ingredient. A 227 g declaration converted back gives 8.007 oz, and a recipe treating that as eight ounces is correct. A 250 g European block converted forward gives 8.82 oz, which is not eight of anything and is the number to use rather than the nearest familiar one.

Gold, silver, platinum and palladium are weighed and priced in troy ounces of 31.1034768 g. That is 9.7 per cent more than the ounce in a kitchen, which means a gram weight of metal converted with the ordinary factor produces about a tenth too many ounces and, multiplied by a spot price, a value that is out by the same proportion.

The tell is usually the context rather than the notation: bullion is quoted "per oz" with no qualifier at all, and a scrap or jewellery weight given in grams needs dividing by 31.1 rather than by 28.35 before it meets that price. The gram figure itself is unambiguous, which is why the metals trade quotes small quantities in grams and leaves the ounce for the headline number.