You're standing in the kitchen. Or maybe you're at a jewelry counter. Perhaps you're just trying to settle a bet with a friend who insists they know the metric system better than you do. You need to know how many grams make a ounce, but the answer depends entirely on what you are weighing.
Standard math says it's 28.35. But that isn't always the truth.
If you are dealing with gold, that number changes. If you are looking at nutritional labels, the government simplifies it. Honestly, the "official" answer is a bit of a moving target depending on the industry. It’s one of those weird quirks of history where the British Imperial system and the French Metric system crashed into each other and left us with a bunch of decimals that nobody can remember without a calculator.
The Standard Answer: 28.3495 Grams
For almost everything you encounter in daily life—sugar, mail, a steak, your cat's flea medication—the world uses the International Avoirdupois Ounce. In 1959, an international agreement among English-speaking nations finally pinned this down. They decided that one pound is exactly 0.45359237 kilograms.
Do the math. Divide that by 16 ounces. You get $28.3495231$ grams.
Most people just round it. 28.35 is the gold standard for home cooks and hobbyists. If you're baking a cake and the recipe calls for an ounce of cocoa powder, hitting 28 grams is plenty close enough. Your brownies won't explode if you're off by half a milligram.
Why the Food Industry Lies to You (A Little)
Check the back of a cereal box. Look at the serving size. You will often see "1 oz (28g)." Notice anything? They dropped the .35.
The FDA in the United States actually allows for some rounding on nutrition labels to make things "user-friendly." They basically decided that consumers don't want to see $28.3495$ on a bag of chips. It’s easier for the brain to process whole numbers. This is fine for a snack, but if you’re a professional baker or a chemist, that 0.35 gram discrepancy adds up fast when you scale a recipe by 100 or 1,000.
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The Troy Ounce: When 28 Grams Isn't Enough
Here is where people get confused. If you go buy a one-ounce gold coin, it will weigh more than an ounce of feathers.
Wait. What?
It sounds like a trick question, but it’s a reality of the precious metals market. Gold, silver, and platinum are measured in Troy Ounces. This system dates back to the Middle Ages, likely named after the French town of Troyes.
A Troy ounce is exactly 31.1034768 grams.
If you try to sell gold based on the 28.35-gram standard, you're losing nearly 10% of your value. That is a massive mistake. When you see the spot price of gold on the news, they are talking about the Troy ounce. Most jewelry scales are specifically calibrated to toggle between "oz" (Avoirdupois) and "ozt" (Troy).
Always double-check the "t" on the screen. It matters.
The Weird World of Fluid Ounces
Let’s be clear: a fluid ounce is not a measurement of weight. It is volume.
People ask how many grams make a ounce when they are looking at a bottle of water, and that is where the physics gets messy. Grams measure mass. Fluid ounces measure how much space something takes up.
A fluid ounce of water weighs approximately 29.57 grams. But a fluid ounce of honey? That’s way heavier because honey is dense. A fluid ounce of rubbing alcohol? Much lighter.
This is why "one cup" of flour weighs differently every time you scoop it. If you pack the flour down, you fit more grams into the same volume. Professional chefs hate volume measurements for this reason. They want everything in grams because a gram is always a gram, regardless of whether you're at sea level or on top of Everest.
How to Convert Like a Pro Without Losing Your Mind
If you don't have a digital scale handy, you have to use conversion factors. It isn't fun. It involves a lot of long-form multiplication that feels like fifth-grade homework.
- To go from Ounces to Grams: Multiply the ounces by 28.35.
- To go from Grams to Ounces: Divide the grams by 28.35.
If you are dealing with large quantities, like kilograms, the errors in rounding become "noisy." For example, if you're shipping a 100-ounce package, that .05 difference between 28.3 and 28.35 turns into 5 grams. That might be the difference between one postage bracket and the next.
Why Does the US Still Use Ounces Anyway?
Most of the world transitioned to the metric system because base-10 math is just easier. 1,000 grams in a kilogram. Simple.
The US stays with the ounce because of infrastructure and stubbornness. Changing every road sign, every nutritional label, and every manufacturing tool would cost billions. So, we live in this hybrid world where we buy soda by the liter but milk by the gallon, and we weigh our mail in ounces but our medicine in milligrams.
It’s messy. It’s confusing. It’s why you’re reading this article.
Common Misconceptions That Mess People Up
One big mistake is assuming that "postal ounces" are different. They aren't. USPS uses the standard 28.35g Avoirdupois ounce. However, their scales are often calibrated to be "sensitive," meaning if you are even a hair over 1.0 ounces, you pay for 2.0.
Another mistake involves "dry ounces" versus "fluid ounces" in cooking. A "dry ounce" is weight (28.35g). A "fluid ounce" is volume ($approx 29.6$ ml). If a recipe says "4 oz shredded cheese," do you use a measuring cup or a scale?
Use a scale.
Shredded cheese is mostly air. If you put it in a 4-ounce measuring cup, you might only be getting 2 ounces of actual cheese. If you weigh out 113 grams (which is $28.35 \times 4$), you get the exact amount of cheese the recipe creator intended.
Practical Steps for Perfect Accuracy
If you want to stop guessing and start measuring correctly, here is the move.
- Buy a Digital Kitchen Scale: You can get a decent one for twenty bucks. Look for one that has a "Tare" function. This lets you put a bowl on the scale, hit the button to reset it to zero, and then measure only the ingredients you add.
- Toggle to Grams: Almost every digital scale has a unit button. Use grams. It's more precise. Most home scales can't accurately show 0.35 of an ounce, but they can easily show 1 gram increments.
- Check the "OZT" Setting: If you are weighing coins or jewelry, ensure the scale says "ozt" for Troy ounces. If it just says "oz," you are getting the wrong reading for precious metals.
- Memorize 28: If you're at the grocery store and just need a "good enough" estimate, remember that an ounce is roughly 30 grams. It’s a slightly high estimate, but it makes mental math easy. If a steak is 300 grams, it’s about 10 ounces. Easy.
Precision counts when it counts. For your morning coffee, 28 grams or 28.35 grams won't change your life. But if you’re compounding medication or trading silver bullion, those decimals are the difference between success and a very expensive mistake. Stick to the 28.35 rule for the physical world and 31.1 for the shiny stuff.
Next Steps for Accuracy
To ensure your measurements are always spot-on, start by calibrating your digital scale using a nickel. A modern US nickel weighs exactly 5.000 grams. If you put a nickel on your scale and it reads 4.8g or 5.2g, you know your device is off, and you should adjust your calculations accordingly. For high-stakes measurements, always default to grams to avoid the rounding errors inherent in the ounce system.