In "Wealth of Nations" Adam Smith tells us that the British pound sterling was defined at least as far back as the time of Edward I as one pound of genuine silver of known purity. Today, sterling silver is still defined much the same way, but can refer to flatware and jewellery, not just money. Silver is "sterling" if it's an alloy of at least 92.5 per cent silver and no more than 7.5 per cent of a base metal (usually copper). To find the price of sterling silver by weight, you must determine how much actual silver is present in an object and then figure its value based on the current sterling silver prices.
Determine the fineness (purity) of the sterling silver. Most sterling silver is 92.5 per cent silver, but some has even higher purity. Check on the object for an embossed hallmark or a jeweller's mark that states the fineness. If you aren't sure, assume the content is 92.5 per cent silver, since that's the minimum an object must contain to be considered sterling.
Weigh the object using a precision scale (the kind used in a chemistry lab is fine). Silver is priced by the Troy ounce, not by regular (Avoirdupois) ounces or grams. So unless your scale is calibrated in Troy ounces, you'll have to convert. There are 31.10 grams or 1.097 regular ounces per Troy ounce. To find Troy ounces, just divide the weight in grams or ounces by the appropriate figure.
Find the amount of actual silver in the object. For example, suppose the item you are examining is a piece of silver jewellery weighing 62.20 grams. Divide 62.20 grams by 31.10 to find the number of Troy ounces (the answer is exactly 2.00 troy ounces). Now multiply the weight in Troy ounces by 92.5 per cent. In this example, that's 2.00 times 92.5 per cent, or 1.85 Troy ounces.
Calculate the value of sterling silver by weight. Go to a website that lists the daily (spot) price of silver bullion (see link under Resources below) to find current sterling silver prices. Let's say the current silver bullion price is £7.80/oz (remember, those are Troy ounces). Using our example from Step 3, multiply 52.4gr by £7.80 to get the value of sterling silver by weight (the answer here is £14.40)
Knowing the value of sterling silver by weight is only part of the story. Jewellery, tableware, and other objects made of sterling silver are often works of high craftsmanship. Their actual market value is greater than the silver itself---often many times greater. If you need to know the real value of sterling silver objects, have them appraised by an expert.