How to Convert Ounces to Grams

Multiply by 28.35. The rounding is never what goes wrong — reading a fluid ounce as a weight ounce is.

What is the formula?

Multiply. To go from ounces to grams:

The exactness is worth a sentence, because it surprises people. 28.349523125 is not the result of anyone weighing anything. In 1959 the United States, the United Kingdom and four other countries agreed that the international avoirdupois pound would be exactly 453.59237 grams. An ounce is defined as one sixteenth of a pound, and 453.59237 ÷ 16 = 28.349523125. The decimal terminates, and it is exact by agreement rather than by measurement.

Ounces to grams conversion table

Weight ounces only. Every figure below is the exact product, with the value you would actually write on a recipe card beside it.

That last row is worth pausing on, because it is where imperial and metric packaging quietly diverge. A one pound pack is 454 g. A 500 g pack is 10.2% larger, not the same thing in different clothes. Going the other way, 500 g is 17.64 oz — a pound and a bit over a half.

How much does the rounding cost you?

Almost nothing, and much less than people fear. Here is every rounding you might plausibly use, with the weight at which it first costs you half a gram.

The practical reading of that table: 28.35 is not an approximation you need to worry about. It is accurate past the capacity of any kitchen scale you own. Most scales round their own display to the nearest gram, which is a far bigger source of error than the conversion factor.

The row that does matter is 28. It is the number people reach for when converting in their head, and it is 1.23% low. On a single ounce that is a third of a gram, invisible. On a 16 oz bread flour weight it is 5.6 g, which in a stiff dough is a noticeable change in hydration.

Is a fluid ounce the same as an ounce?

No, and this is where recipes actually go wrong. A weight ounce measures mass. A fluid ounce measures volume. They share a name and nothing else. The reason the confusion survives is that for water they happen to be close — and water is the one ingredient people test the rule on.

One US fluid ounce is 29.5735 millilitres. What that volume weighs depends entirely on what is in it:

There is a neat historical footnote hiding in that table. The imperial fluid ounce, still used in the UK, is 28.4130625 mL — so one imperial fluid ounce of water weighs about 28.41 g, against a weight ounce of 28.35 g. The two agree to 0.22%. That is by design: the imperial fluid ounce was defined as the volume occupied by one ounce of water. The US fluid ounce descends from a different, older gallon and does not share the property, which is why the same phrase means slightly different amounts on either side of the Atlantic.

Converting grams back to ounces

Divide by 28.349523125, or multiply by 0.03527396. In practice, dividing by 28.35 is easier to remember and just as accurate.

A quick sanity check worth keeping: 16 oz should land near 454 g. If a converted figure claims to be about a pound and comes out near 500 g, a fluid ounce has been treated as a weight ounce somewhere in the chain.

Why is a troy ounce different?

Because it is a survivor from a separate system. The troy ounce is 31.1034768 grams and is used today for one purpose: pricing precious metals. It is 9.714% heavier than the avoirdupois ounce you use for food.

The practical consequence: a gram figure for gold is 9.7% larger than the same number of everyday ounces would suggest. Use the wrong ounce on a one-kilogram bar and you are out by more than three troy ounces. Prices quoted “per ounce” for metal always mean troy; prices per ounce for anything else never do.

A worked example: one recipe, three ways to get it wrong

A US recipe calls for 8 oz all-purpose flour, 4 oz butter and 6 fl oz milk. You want it in grams. Here is what each reading produces.

Read the bottom row from right to left. The 28-in-your-head shortcut costs 0.8%, which no one will taste. Mixing up the ounces costs 20.5% — a fifth of the batch — and it lands almost entirely on the flour, so the dough behaves like a different recipe. This is the whole point of the guide: the arithmetic is not the risk, the unit is.

Note also what the correct column does with the milk. Six US fluid ounces is 177.4 mL, and milk is about 1.03 g/mL, so it weighs 182.8 g — not the 170.1 g that 6 × 28.35 would give you.

Terms worth knowing

Avoirdupois

The everyday mass system: 16 ounces to the pound. Unless a context says otherwise, an ounce is this one.

Troy ounce

31.1034768 g. Twelve troy ounces make a troy pound, which is why nothing about the troy system lines up with the everyday one.

Fluid ounce

A unit of volume, not mass. 29.5735 mL in the US, 28.4130625 mL imperial. Written fl oz when anyone is being careful.

Density

Mass per unit volume, usually g/mL for cooking. The bridge between a fluid ounce and a gram, and the reason there is no single answer.

International pound

Exactly 453.59237 g by the 1959 agreement between the US, UK, Canada, Australia, New Zealand and South Africa. Every ounce figure on this page descends from it.

Tare

Zeroing a scale with the empty bowl on it, so it reads only what you add. The reason weighing beats measuring by volume for dry goods.

Scooped vs spooned

Two ways to fill a cup with flour. Scooping compacts it: about 142 g per cup against roughly 120 g spooned and levelled, an 18% spread from the same cup.

All 14 converters in this guide

Authoritative sources

• Unit conversion — NIST Office of Weights and Measures — the US authority for the exact factors used on this page.
• International yard and pound — Wikipedia — the 1959 agreement that fixed the pound at exactly 453.59237 g.
• Troy weight — Wikipedia — where the 31.1034768 g ounce comes from and why it survived.
• Fluid ounce — Wikipedia — the US and imperial definitions, and why they differ.
• The SI — BIPM — the definition of the kilogram that anchors the gram.

Last updated: 2026-09-01 · Published: 2024-03-18 · Written by the miniwebtool.com editorial team.

This guide is for general and educational use. The conversion factors are exact by definition and can be checked against the sources above. Ingredient densities are typical values and vary with brand, humidity, temperature and how a cup was filled — treat the fluid-ounce weights as close estimates, not specifications. Where a recipe's outcome matters, weigh the ingredient rather than converting a volume figure.