How to Find Out Your Partner's Ring Size Without Ruining the Surprise
Finding out your partner's ring size without asking them directly — and without revealing that a proposal is being planned — is one of the more practically challenging parts of commissioning a surprise engagement ring. The good news is that ring sizing can be adjusted after delivery, and the strategies for getting close to the right size without ruining the surprise are more reliable than most people expect.
TL;DR: The most reliable way to find a partner's ring size secretly is to borrow an existing ring they wear on the fourth finger of their left hand and have it measured by a jeweller. If no existing ring is available, a UK size L to M is the most common women's ring finger size and a reasonable starting estimate. Most bespoke rings can be resized by one to two sizes after delivery if the initial size is slightly off.
The Most Reliable Method: Borrowing an Existing Ring
If your partner wears a ring on the fourth finger of their left hand — the finger the engagement ring will be worn on — borrowing it temporarily and having it measured by a jeweller is the most accurate method. A jeweller can measure the internal diameter of a ring in seconds and give you the corresponding UK size.
The timing of borrowing the ring matters. Taking it while your partner is asleep, borrowing it for a day while they are at work, or taking it for cleaning and having it sized in the process all work as approaches. The ring needs to be the one worn specifically on the left hand fourth finger for the measurement to be relevant — rings are worn at different positions on the hand and the finger sizes can differ by a full size or more.
Making a Size Impression at Home
If borrowing the actual ring is not feasible, pressing it into a bar of soap or a piece of modelling clay creates an impression of the internal diameter that a jeweller can measure. Alternatively, tracing the inside of the ring onto a piece of paper and measuring the resulting circle with a ruler gives the internal diameter in millimetres, which can be converted to a UK ring size using a standard conversion chart. Our ring sizing page has the full conversion table.
Asking Indirectly
Asking a partner's close friend or sibling is a reliable approach if you have someone who can be trusted completely not to mention it. The question can be framed as general interest in jewellery rather than a direct request, making it slightly less obvious. The friend or sibling can ask your partner to try on a ring of theirs and remember the size, or simply ask if they happen to know their ring size.
The Ring Sizer Method
Ring sizer sets — a set of numbered metal or plastic rings covering the full UK size range — are available online for a few pounds. Leaving one in an accessible location and noting which size your partner tries on, or asking them casually to try it during a conversation about someone else's jewellery, is a low-risk approach that does not require access to their existing jewellery.
What to Do If You Cannot Find the Size
If none of the above is feasible, a UK size L is a good starting point for most women: it represents the average UK women's ring finger size and fits a broad range of hands. If your partner has noticeably slender or broad hands, adjusting one size in either direction is reasonable.
Most bespoke engagement rings at À Vie Diamonds can be resized by one to two sizes after delivery within our complimentary resize window (three months from delivery for most designs). A ring that is slightly too large or too small at delivery is not a crisis — it is a normal part of the bespoke process when sizing information is unavailable before production. We discuss this explicitly at the brief stage for surprise commissions.
See our ring sizing page, our aftercare page, and get in touch to discuss a commission.
Frequently Asked Questions
What is the average women's ring size in the UK? UK size L to M is the most common range for the ring finger. This corresponds to approximately 51mm to 52mm internal circumference. Individual variation is significant, and the average is only a useful starting point when no other information is available.
Can an engagement ring be resized after purchase? Most plain band engagement rings can be resized by one to two sizes after production. Full eternity rings and rings with continuous pavé around the band cannot be conventionally resized. À Vie Diamonds includes a complimentary resize within three months of delivery for most designs.
How do I measure ring size at home? The internal diameter of an existing ring in millimetres, converted to a UK letter size using a standard chart, is the most practical home measurement. Our ring sizing guide has the full conversion table and additional measurement methods.
Last reviewed: July 2026 · À Vie Diamonds