The moment you decide to propose is thrilling — but one detail can make or break the surprise: getting the ring size right. A ring that's too loose will spin around their finger, while one that's too tight will be uncomfortable or impossible to wear. Yet asking directly ruins the entire surprise. The good news? There are several clever ways to discover their ring size without raising suspicion.
This guide covers seven proven methods used by couples planning proposals, plus expert tips on handling sizing mishaps and what to do if you're still uncertain.
Why Getting the Right Size Matters
Getting the correct ring size is one of the most important aspects of a surprise proposal. Here's why it matters so much:
Wrong size ruins the emotional moment
If the ring doesn't fit, your partner has to take it off immediately. Instead of admiring their engagement ring, they're preoccupied with a poor fit. That magical first moment gets overshadowed.
Resizing can take weeks
Professional resizing typically takes 2–4 weeks. Imagine getting engaged and not being able to wear the ring immediately. Your partner will want to show it off right away.
Some ring styles can't be resized
Eternity bands (which have diamonds all the way around) and tension settings are extremely difficult or impossible to resize. Getting the size right the first time is essential with these styles.
7 Ways to Secretly Measure Ring Size
Here are the most effective methods to discover your partner's ring size without arousing suspicion:
1. Borrow a Ring They Already Wear
The easiest method is to take a ring your partner already owns and wears regularly. This is the most accurate approach because you're getting a direct measurement from a ring they find comfortable.
How to do it:
- • Take a ring from their jewelry box that they wear on their right hand ring finger (the left hand ring finger is usually slightly smaller, so the right-hand measurement is safer)
- • Download the MyRingSizer app on your phone
- • Place the ring on your phone screen and let the app measure it instantly
- • Return the ring to their jewelry box before they notice it's gone
Pro tip: The best time to do this is when they're distracted or away from home for a few hours.
2. Use the String Method While They Sleep
This subtle method works when your partner is asleep. It requires a thin strip of paper or string, a marker, and a ruler — nothing they'll suspect if discovered.
How to do it:
- • Wrap a thin strip of paper or soft string around their ring finger while they're asleep
- • Mark where the paper/string overlaps with a pen
- • Carefully remove the paper and lay it flat
- • Measure the circumference in millimeters with a ruler
- • Use our ring size chart to convert the circumference to a US size
Pro tip: Be very gentle to avoid waking them. The measurement should feel like the ring fits comfortably — not too loose or tight.
3. Trace a Ring on Paper
This visual method gives you a quick reference without needing any special tools. You only need a piece of paper, a pen, and a ruler.
How to do it:
- • Place one of their rings flat on a piece of white paper
- • Trace the inner circle carefully with a pen
- • Measure the diameter of the circle with a ruler in millimeters
- • Use this quick reference: US 6 = 16.5mm, US 7 = 17.3mm, US 8 = 18.1mm
Pro tip: Measure from the inside edge of the ring, as the outer diameter will be larger and less accurate.
4. Ask Their Friends or Family
Trusted friends or family members may already know your partner's ring size — or they can help you find out discreetly without revealing your plans.
How to do it:
- • Confide in a close friend or family member who knows about your proposal plans
- • Ask them to casually mention trying on rings together "for fun"
- • They can observe which size feels comfortable or ask directly in a casual way
- • Report back to you with the size information
Pro tip: Choose someone your partner is comfortable with and who can naturally bring up the topic without raising suspicion.
5. Use the MyRingSizer App on Their Phone
If you have brief access to your partner's phone, you can download the MyRingSizer app, measure one of their existing rings, and delete the app afterward.
How to do it:
- • Download the MyRingSizer app from the App Store on their phone
- • Borrow one of their existing rings (or find a photo of measurements)
- • Place the ring on the phone screen and take the measurement
- • Screenshot the result for your records
- • Delete the app from their phone to keep your secret safe
Pro tip: Alternatively, use your own phone with one of their rings — this leaves no trace on their device.
6. Compare to Your Own Fingers
If you have a similar hand size to your partner, you can use your own fingers as a reference point for indirect measurement.
How to do it:
- • Try one of their rings on your fingers and note which one it fits best
- • Use the MyRingSizer app to measure that finger on your own hand
- • Account for the small difference in hand size and adjust accordingly
Pro tip: This method is less precise but can give you a ballpark estimate if other methods aren't available.
7. Buy a Ring Sizer Set
Plastic ring sizer sets are inexpensive and can be left around your home or given as a "fun gift" without raising major suspicion.
How to do it:
- • Purchase an inexpensive plastic ring sizer set from Amazon or a jewelry store
- • Leave it around the house casually or give it as a "fun gift" with a laughing explanation
- • Suggest they try it on "just for fun" or while you're shopping
- • Observe which size fits comfortably on their ring finger
Pro tip: Frame this as curiosity about ring sizes in general, not specifically about them.
What If You Get the Wrong Size?
Don't panic if you discover after the proposal that the ring doesn't fit perfectly. Here's what you need to know:
Most jewelers offer free resizing
Many jewelers provide free resizing within 30–60 days of purchase. Check your purchase receipt for the resizing policy. Professional resizing typically costs $50–150 if not covered.
Size up if you're unsure
If you're uncertain between two sizes, it's generally safer to size up slightly. A ring that's slightly loose can be adjusted and is more comfortable than one that's too tight. Sizing down is more disruptive to the ring's design.
Avoid certain styles for surprise proposals
If there's any uncertainty about size, avoid eternity bands and tension settings. These rings cannot be resized without damaging the design. Opt for more traditional settings that can be easily resized if needed.
Ring Size Tips for Engagement Rings
Keep these important factors in mind when determining your partner's engagement ring size:
Left hand ring finger is standard
Engagement rings are worn on the left hand ring finger in most Western cultures. This finger is typically slightly smaller than the right hand ring finger.
Left hand is usually smaller
If you measured their right hand ring, account for the fact that their left hand is typically 0.5 sizes smaller. If their right hand is a US 7, the left is likely a US 6.5.
Measure at the end of the day
Fingers are slightly larger in the evening due to normal daily swelling and activity. This gives you the safest measurement for daily wear.
Account for knuckle size
If their knuckle is noticeably larger than their finger base, find a size between the two measurements. The ring should slide over the knuckle without excessive force.
Wide bands need sizing up
Engagement rings with bands 6mm or wider may need a half-size larger for comfort. Wide bands sit differently on the finger than thin bands.
Temperature affects size
Cold temperatures shrink fingers, warm temperatures enlarge them. Measure in moderate conditions, not on the coldest or hottest days.
Average Engagement Ring Sizes
If you have no other information and need to make an educated guess, here are the average engagement ring sizes:
Women's Average
US 6 to US 7
16.5mm to 17.3mm diameter
This covers approximately 60% of women
Men's Average
US 9 to US 10
18.9mm to 19.8mm diameter
For men's wedding bands and rings
Note: These are just starting points if you're guessing. The methods above will give you much more accurate results specific to your partner.
Download MyRingSizer for Instant Measurements
The easiest way to measure ring size is with the MyRingSizer app. Place any ring on your phone screen and get an instant, accurate size in seconds — no math required.
Frequently Asked Questions
Can I measure a ring size on my phone?
Yes! The MyRingSizer app is specifically designed to measure ring sizes on your phone. Simply place any ring on your phone screen, and the app will measure the inner diameter and convert it to your ring size. It's accurate and takes just a few seconds.
What's the most common engagement ring size?
The most common engagement ring size for women in the US is between a US 6 and US 7, with US 7 being the single most popular size. However, ring sizes vary significantly based on age, hand size, and individual differences. Using one of the methods in this guide will give you a much more accurate measurement for your partner.
Should I size up or down if I'm unsure?
Always size up if you're uncertain between two sizes. A ring that's slightly loose is more comfortable and can be adjusted by a jeweler more easily than a ring that's too tight. A tight ring can cut off circulation and is uncomfortable to wear daily. Jewelers can size down a ring more easily than sizing up for certain designs.
Can all rings be resized?
Most rings can be resized, but not all. Eternity bands (rings with diamonds all the way around) and tension settings are extremely difficult or impossible to resize without damaging the design. If you're purchasing a ring with either of these designs for a surprise proposal, getting the size exactly right is crucial.
How accurate is the MyRingSizer app?
The MyRingSizer app is highly accurate when used correctly. It measures the inner diameter of a ring using your phone's camera and advanced calibration technology. For best results, use a ring they wear regularly on the same finger where they'll wear the engagement ring, and measure in good lighting. Accuracy is typically within 0.1mm, which is precise enough for reliable ring sizing.
