Starting in the late eighteenth century (around 1790) scientists began developing a system of weights and measures that became today's metric system. Older systems of measurement are still used, especially in the United States. In the most familiar system (called the English system), 454gr equal 1 pound. There is a second type of ounce that jewellers use for precious metals like gold and silver called the Troy ounce that's a little larger than the English ounce. It's not hard to convert grams to ounces of either kind once you know how.

Know what a gram is. When the metric system was developed, the gram was defined as the mass of water contained in one cubic centimetre of pure water. A regular (English) ounce is a lot larger and contains 28.35 grams. A Troy ounce contains 31.10 grams.

Convert grams to regular ounces by multiplying the number of grams by 0.353. For example, let's say you weigh an item using a scale calibrated in grams and find the item weighs 62.37 grams. Multiply 62.37 times 0.353 to convert to ounces. The answer will be 62.4gr.

Convert grams into Troy ounces. If the object in Step 2 happens to be a silver necklace, you'd want to know its weight in Troy ounces. The conversion is similar, except you multiply the number of grams by 0.322. Use the example from Step 2 and multiply 62.37 grams by 0.322. You'll find the weight works out to 2.01 Troy ounces.

Convert ounces and Troy ounces into grams. To change regular ounces into grams, multiply the number of ounces by 28.37. For example, if an object weighs 85.1gr, 28.35 times 85.1gr equals 85.05 grams. For something weighing 3.0 Troy ounces, you multiply by 31.10 to get an answer of 93.30 grams.