A ring is the correct size when you don't feel it on your finger, yet it's not loose. Stretching a ring requires a ring mandrel and a jewellery hammer. It's worth it to own these tools if you need to stretch rings often. If your ring has stones set in the band, you should have it professionally resized. You can resize a ring with a diamond if you're only going up less than one full size.
Measure your finger using a ring gauge, or lay your ring on a ring chart to determine the size you need. You can also download a paper ring sizer (see Resources). Choose a size that slips on easily and feels snug on your finger, but not tight. The ring should not easily shift between the knuckles. You can also have your finger measured by a jeweller.
Place the ring on a mandrel -- a steel tool shaped like a rod, used for shaping and resizing rings -- and cover the ring with an inexpensive, soft, microfiber cloth to prevent dents and scratches.
Tap the ring with a rawhide jewellery mallet. Unlike an ordinary hammer, a rawhide mallet will not dent or scratch metal. Distribute the taps evenly around the entire ring. Never tap the settings or stones. You will notice the ring stretching gradually as it moves down the mandrel shaft.
Try the ring on after every few taps. If it stretches too much, you cannot make it smaller at home.
Heating your ring with an annealing torch will soften the metal, making it easier to stretch. Never anneal a ring with diamonds, coloured gems or other stones.
Do not enlarge your ring more than one full size because you can stretch and damage your settings. Going up more than one size requires removing all of the stones. It's risky to resize a wedding ring with stones because you can damage the settings. The price of repairing a damaged setting is much higher than paying a jeweller to resize your wedding ring professionally. Making a ring smaller requires cutting away part of the band and seamlessly resoldering it. Attempt this yourself only if you have experience.