How do I find a woman's ring size?

Start with a paper or plastic ring sizer, which most jewellers will send you free or for a small cost. Wrap it around the base of the finger, and make sure it slides over the knuckle but feels snug. If you already have a ring she wears on that finger, place it over a ring gauge or measure the inside diameter with a ruler, then compare with a size chart.

For a surprise, you need to be clever. Ask her mum, sister or best friend if they know her size, or borrow a ring from her jewellery box for a day. Avoid guessing from shoe size or height, because rings vary by finger and hand shape. Remember that fingers swell in heat and shrink in cold, so measure at room temperature and later in the day. If you are between sizes, go for the larger one, especially for a wide band.

Keep in mind that her size may change over time, for example with pregnancy, weight change or medication. Most jewellers will resize a plain band easily, so do not worry if the first size is not exact. Just be honest with the jeweller that it is a surprise, and they will often help you plan.