Grams to ounces or ounces to grams 28 grams to the ounce is commonplace. But it’s wrong. An ounce actually weighs 28.349523125 grams. And it doesn’t matter if you’re weighing weed, water melons or weather vanes when it comes down to it—an ounce of weed isn’t 28 grams. It’s more. In fact it’s .349 grams more.