12 February 2026 · 7 min read
How to Find Her Ring Size Without Her Knowing
A surprise proposal is one of the most romantic things you can do — and one of the most logistically tricky, because the one piece of information you absolutely need is the one you cannot ask for. The good news: there are several reliable ways to find your partner's ring size without giving the surprise away, and a couple of safety nets if your guess turns out to be wrong. This guide walks through every method, ranked by how reliable it actually is in practice.
The Honest First Option: Just Ask Someone Close
Before any clever tricks, ask yourself: who in her life would know? Her sister, her mum, her best friend, or her flatmate is often the simplest answer. If she has ever bought rings together with someone, that person almost certainly remembers roughly what size she wears. A trusted friend or family member can also discreetly go shopping with her, “try on rings for fun,” and find out exactly.
This is the highest-reliability method by a wide margin. Most surprise proposals where the ring fits perfectly involve a sister or mother quietly being read in.
The Borrowed Ring Trick (Most Accurate DIY Method)
If you can get hold of a ring she already wears — even for just a few hours — any jeweller in New Zealand can size it for you in under a minute. This is by far the most accurate DIY method.
The critical detail: the borrowed ring must come from the correct finger. Most women wear engagement rings on the fourth finger of the left hand (the “ring finger”). Borrowing a ring she wears on her index finger or right hand will give you the wrong size — usually too large.
Bring the ring to one of our showrooms and we will measure it on the spot, no appointment needed. You can have it back the same day.
Tips for borrowing without notice
- ✓ Take a ring she wears infrequently — she won't miss it
- ✓ Confirm which finger she wears it on
- ✓ Photograph the inside before removing it (in case of stamps you need to remember)
- ✓ Return it before she notices it is gone
The Trace-and-Measure Method
If you cannot bring the ring to a jeweller — for example, you only have a few minutes alone with it — trace the inside of the ring on a piece of paper and measure the diameter in millimetres. A standard NZ size M is around 16.7mm internal diameter, size N around 17.1mm, and size O around 17.5mm. Each size up adds roughly 0.4mm of diameter.
The internal diameter table below covers the most common women's sizes in New Zealand:
| NZ size | Internal diameter | US equivalent |
|---|---|---|
| J | 15.4 mm | 5 |
| K | 15.8 mm | 5.25 |
| L | 16.3 mm | 5.75 |
| M | 16.7 mm | 6.25 |
| N | 17.1 mm | 6.75 |
| O | 17.5 mm | 7.25 |
| P | 17.9 mm | 7.75 |
The String Method (and Why It Often Fails)
You may have read advice to wrap a piece of string around her finger while she is sleeping. We do not recommend it. String stretches, fingers swell at night, and even small measurement errors translate into a ring that does not fit. We have seen far more proposals saved by the borrowed-ring method than by any string trick.
If string is genuinely your only option, use a thin strip of paper instead, mark the overlap with a pen, and bring it to a jeweller for measurement — but treat the result as a starting point, not gospel.
The “Pretend It's for You” Tactic
If you simply cannot get her ring size any other way, try the casual conversation approach. Mention that a friend asked you what your ring size is. Ask hers in return — “I have no idea, do you know yours?” Many women genuinely do know their size, especially if they wear rings regularly.
Alternatively, take her shopping for “a costume ring” or a fashion ring as a present and let the assistant size her finger. The tactic only works once, and works best if she is not currently expecting a proposal.
NZ Ring Sizes — A Quick Note
New Zealand and Australia use an alphabetical sizing system inherited from the UK — A through Z, with halves between letters. The most common women's engagement ring sizes in New Zealand are between L and P, with the average sitting around N. The most common men's wedding band sizes are between R and V.
If you are buying from an overseas retailer, double-check the sizing system — American (numeric) and European (millimetres) sizes do not map cleanly onto the NZ alphabet. The conversion table above will help.
What If You Guess Wrong?
Take a breath — this is more common than you think, and it is fixable. Most rings can be resized up or down by two full sizes without affecting their structure or appearance. At Diamond Rings NZ, the first resize after purchase is free of charge — so if your guess is off, the only cost is a few days without the ring.
If you are completely unsure, our advice is to err slightly on the larger side. It is much easier to wear a ring that is slightly loose for a week or two than to wear one that does not fit at all. And the moment you propose, the ring just needs to slip on the finger — perfect fit can be sorted afterwards.
If you would like more guidance on the bigger picture, our complete engagement ring guide covers shape, setting, metal, and budget alongside sizing.
Need help with sizing or planning a surprise?
Bring a borrowed ring into one of our showrooms in Auckland, Wellington or Christchurch and we will size it for you on the spot. First resize after purchase is on us.