1. To purchase a very low value well fitting ring and try its fit during a day or so, or,2. To approach a jeweler/jewelry-chain trying their sizing kit. It is advisable to have trials on two occasions (fingers may change diameter during the day cycle, e.g., morning vs. evening).
Establish this comfortable and secure fit and its actual size-number in American standards (most jewelers will have conversion tables from European, British, or Japanese ring sizing units to US standards. If not, include your local size in the Order Form's message window as fully and accurately as possible and communicate it to us, once certain.
Unlike size units such as inches, pounds or gallons, ring sizes are NOT standardized, regulated or controlled. Different kits may vary the upward of 1/4 to 1/2 size! Exchanges due to size issues might be costly to you in S&H charges, and will not entitle you to automatic refund. Resizing in Titanium is next to impossible (it is only possible, to a limited extent, on the upwards side). While you may still submit your order temporarily with a tentative size, on a "best known" size basis, so that your ring is lined up for production, you should determine and submit the right size within a couple of days from preliminary submission. In fact, once you submit your order our answer will include further tips for determining your ring size. You may wish to consider also sending us another ring that fits the wearer-to-be well for sure sizing purposes. We will proceed to custom-manufacture your order to the sent sample's exact size, and to return it to you together with your ordered ring(s). No diamond rings as samples, please...
P.S. Tip: If the ring is to be a surprise try, somehow, to discretely borrow one of her rings which you have observed previously to have been worn comfortably by her (on the right finger!) and size it, or, you may try to obtain the information, discretely, through a third party...