How to Convert Ounces to Grams
Learn how to convert ounces to grams for cooking, nutrition, and shipping using the exact conversion factor of 28.3495 g per ounce. Covers avoirdupois, troy, and fluid ounces.
The Standard Conversion Factor
1 avoirdupois ounce (oz) = 28.3495 grams (g). This is the ounce used in everyday US and UK weight measurement for food, body weight, and packages. Conversely, 1 gram = 0.035274 ounces. These values are exact derivations from the defined pound: 1 lb = 453.59237 g, and 1 oz = 1/16 lb.
Ounces to Grams Formula
Grams = Ounces × 28.3495. Converting a 16 oz (1 lb) bag of flour: 16 × 28.3495 = 453.6 g. A 4 oz serving of meat: 4 × 28.3495 ≈ 113.4 g. For quick mental math, multiply ounces by 28 or 28.35; the approximation error is less than 0.2 %.
Grams to Ounces Formula
Ounces = Grams ÷ 28.3495. A 100 g chocolate bar: 100 ÷ 28.3495 ≈ 3.53 oz. A 500 g bag of pasta: 500 ÷ 28.3495 ≈ 17.64 oz ≈ 1.1 lbs. Nutritional labels in the US often show serving sizes in grams even on products sold by the pound, so this reverse conversion is frequently needed.
Avoirdupois vs. Troy Ounces
The troy ounce (troy oz or ozt) is used exclusively for precious metals (gold, silver, platinum) and equals 31.1035 g — about 10 % heavier than the avoirdupois ounce. Gold prices are quoted per troy ounce worldwide. If you are converting precious metal weights, use 1 troy oz = 31.1035 g, not 28.3495 g, or the error will significantly affect financial calculations.
Fluid Ounces vs. Weight Ounces
Fluid ounces (fl oz) measure volume, not weight. 1 US fluid ounce = 29.5735 mL. Water happens to weigh approximately 1 oz per fluid ounce (29.57 g vs. 28.35 g), but other liquids differ: honey weighs about 1.4 oz per fluid ounce. Never substitute fluid ounces for weight ounces in a recipe without checking the substance's density.
Cooking and Recipe Conversions
Professional baking recipes from European sources list ingredients in grams for precision; US recipes often use cups and ounces. Common conversions: 1 cup of all-purpose flour ≈ 120–130 g ≈ 4.2–4.6 oz; 1 cup of granulated sugar ≈ 200 g ≈ 7.05 oz; 1 cup of butter ≈ 227 g ≈ 8 oz. A kitchen scale set to grams eliminates the imprecision of volume measurements.
Postage and Shipping
US postage rates are calculated by the ounce for light letters and packages. USPS first-class mail allows up to 3.5 oz for letters; above that, package rates apply. International shipping regulations often specify weight limits in grams or kilograms, so converting between ounces and grams is necessary when mailing items abroad or calculating customs documentation.
Try These Calculators
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