How Many Grams in an Ounce

One ounce is 28.35 grams — or, to be exact about it, 28.349523125. That precision is the interesting part. Run the same search and you'll be told 28, 28.3, 28.35 and 28.4 by four different pages, none of them quite agreeing. They're all rounding the same fixed number, and which rounding you reach for only matters in a few specific places — one of which can cost you real money.

For anything you'll actually do in a kitchen, 28 grams is close enough and easy to hold in your head. The tool below gives you the exact figure for any amount and shows, side by side, how far each common shortcut drifts as the quantity climbs.

Why it's such an awkward number

The ounce wasn't designed around the gram, so the conversion was never going to land on something tidy. Since 1959 the avoirdupois pound — the everyday pound behind food, post and bathroom scales — has been defined as exactly 0.45359237 kilograms by international agreement. An ounce is one-sixteenth of that, which works out to 28.349523125 grams: exact, but ugly. Every "28.35" you see is that figure rounded to two decimals; every "28" is it rounded to none. The number isn't uncertain or disputed — it's just inconvenient, so everyone trims it to a different length.

When the rounding actually bites

Three places. In cooking, it never matters — half a gram across an ounce of butter is invisible in the result, so round to 28 and move on. In medicine and supplements, it can matter a great deal: dosages are calculated to the milligram, and a US nutrition label legally treats one ounce as exactly 28 grams under FDA rounding rules, so the "28" there is a regulation, not a guess. And in precious metals it matters most of all — but for a second reason as well as precision: gold, silver and platinum aren't weighed in this ounce at all. They use the heavier troy ounce of 31.10 grams, which is a different unit with a different story. That one is covered in full on ounces in a pound.

The most-converted weight on the internet

Grams in an ounce is one of the single most-searched conversions there is, and the reason is a standoff. Most of the world weighs in grams; the United States, and recipe writers everywhere who learned from it, still weigh small amounts in ounces. So the ounce has become the last imperial weight unit a metric cook regularly meets — on an imported recipe, a coffee bag, a US food label — and the gram is the unit they want it back in. The conversion sits exactly on the seam between the two systems, which is why it never stops being googled.

One ounce that isn't grams at all

A quick warning, because it trips people up: the fluid ounce measures volume, not weight, and does not convert to grams on its own. A fluid ounce of honey and a fluid ounce of water weigh different amounts, because grams depend on what you're weighing. If your recipe says “fl oz,” you're in a different question — see ounces in a cup.

Quick reference

For gold and other precious metals, use the troy ounce (31.10 g) instead.

Sources

• International Yard and Pound Agreement (1959) — avoirdupois pound = 0.45359237 kg exactly; 1 oz = 1/16 lb = 28.349523125 g. Figures as published by NIST.
• US FDA, 21 CFR 101.9 — for nutrition labeling, one ounce is treated as 28 g.
• Troy ounce = 31.1034768 g — Royal Mint / London Bullion Market Association; covered on the ounces-in-a-pound page.

Related

• How Many Ounces in a Pound — and the troy/gold story
• How Many Ounces in a Cup
• How Many Grams in a Kilogram
• How Many Kilograms in a Pound
• How Many Grams of Sugar in a Teaspoon
• How Many Conversions Are There
• Measurements & Conversions Hub

The number never changes — 28.349523125, the same in every kitchen on Earth. The only real decision is how much of it you bother to keep.