Ring size is the detail that most often turns a good decision into a return. It is also entirely measurable at home, provided you avoid the two mistakes almost everyone makes: measuring at the wrong time of day, and forgetting that the knuckle, not the base of the finger, decides whether a ring goes on.
Before you measure: three things that change the answer
Temperature. Fingers shrink in cold and swell in heat. A measurement taken with cold hands can be half a size small. Measure when your hands are warm and at rest.
Time of day. Fingers are typically at their largest in the late afternoon and evening, and smallest first thing in the morning. Late in the day is the more useful measurement, because that is when a ring is most likely to feel tight.
The knuckle. The ring has to pass the knuckle and then sit on the finger without spinning freely. If your knuckle is much larger than the base of your finger, size to the knuckle and accept a slightly looser fit below it.
Method 1: measure a ring that already fits
This is the most accurate method available at home, and the one to use if you can.
Take a ring already worn on the intended finger. Measure the inside diameter across the widest point with a ruler, in millimetres. Be precise – a third of a millimetre is roughly a quarter size.
Compare against these US sizes:
Size 4 is 14.9 mm. Size 5 is 15.7 mm. Size 6 is 16.5 mm. Size 7 is 17.3 mm. Size 8 is 18.1 mm. Size 9 is 18.9 mm. Size 10 is 19.8 mm.
Half sizes fall between, roughly 0.4 mm apart. If your measurement lands between two, go up rather than down.
Method 2: string or paper strip
Use this when there is no existing ring to copy.
Cut a strip of paper about 6 mm wide, or take a length of non-stretch string. Wrap it around the base of the finger, snug but not tight, and mark where it overlaps. Take it off, lay it flat, and measure the length to your mark in millimetres. That is your circumference.
Convert using these US sizes:
Size 4 is 46.8 mm. Size 5 is 49.3 mm. Size 6 is 51.9 mm. Size 7 is 54.4 mm. Size 8 is 57.0 mm. Size 9 is 59.5 mm. Size 10 is 62.1 mm.
Then check the strip passes over the knuckle at that length before you trust it.
Avoid elastic, thread that stretches, or anything you have pulled tight. Every one of those reads small.
Method 3: a jeweler’s ring sizer
The most reliable option overall is a physical sizer – a set of graduated metal rings or a plastic sizing gauge. Any jeweler will size you free of charge in a couple of minutes, and inexpensive plastic sizers are widely available if you would rather do it privately.
If the ring is a surprise, this is also the discreet route: a jeweler can size a ring you have borrowed without you needing to explain anything.
How to size a ring as a surprise
Borrow a ring she wears on the correct finger, ideally one she is not wearing that day, and measure it with method 1. Note which finger it came from – ring sizes commonly differ by a full size between hands, and the dominant hand is usually slightly larger.
If borrowing is impossible, press one of her rings into a bar of soap or a piece of soft clay to take an impression, and measure the impression’s inside diameter.
As a last resort, US women’s ring sizes cluster around 5 to 7 and men’s around 9 to 11. This is a genuinely poor substitute for measuring, and you should treat it as a starting point for a ring you expect to resize rather than a size you are confident in.
Width changes the size you need
A wide band covers more of the finger and feels tighter than a narrow one at the same nominal size. As a rule of thumb, for a band around 6 mm or wider, consider going up a half size. Comfort-fit bands, which are domed on the inside, run slightly more generous and often fit true or a touch large.
Before you order
Check whether the specific design can be resized. Plain and solitaire bands usually can. Eternity bands, channel-set and full pave designs frequently cannot, because the stones run through the area a jeweler would need to cut. Where a piece cannot be resized, getting the size right at the point of order is the only option, and our 30-day return policy is the fallback.
Every ring in the collection lists the sizes available on its product page. Browse engagement rings, wedding bands or rings for women, and if you are unsure about a specific design, ask us before ordering.
Read next
How to Choose an Engagement Ring – the order to make decisions in.
10K vs 14K vs 18K Gold – which karat survives daily wear.
How to Choose a Diamond: the 4Cs – what drives a stone’s price.
