How to Find Her Ring Size in Secret: A Practical Guide to Engagement Rings That Fit

The most reliable way to find her ring size in secret is to borrow a ring she already wears on her ring finger and have a jeweler measure it. If that is not possible, measure the inside diameter of that ring yourself and read the size from a chart. Engagement rings can usually be adjusted by up to two sizes afterwards, so the goal is to get close, not perfect.

Six Ways to Find Her Size, Ranked by Accuracy

Method	Accuracy	Risk of being caught
1. Take one of her rings to a jeweler	Highest	Medium
2. Measure the inside diameter of her ring	High	Low
3. Trace or press her ring	Good	Low
4. Ask someone who knows	Good, if they really know	Depends on the person
5. Try her ring on your own finger	Fair	Low
6. Measure her finger while she sleeps	Poor	High

1. Take one of her rings to a jeweler. Choose a ring she wears on the ring finger of her left hand, or one she will not miss for an hour. The jeweler slides it onto a sizing mandrel and reads the size in seconds. Return it to the exact spot you found it.

2. Measure the inside diameter. Lay the ring flat and measure straight across the inside, edge to edge, with a ruler or, better, a digital caliper. Measure in millimeters and take the reading twice. A fraction of a millimeter matters: half a size is only 0.4 mm.

3. Trace or press the ring. Place the ring on paper and trace the inside circle with a sharp pencil, several times. Or press the ring into a bar of soap or a piece of modeling clay to leave an impression. A jeweler can read a size from either.

4. Ask someone who knows. Her mother, sister or closest friend may know her size or can find out during a casual shopping trip. Pick someone who can keep a secret, and ask which finger and hand the size refers to.

5. Try her ring on your own finger. Slide it onto whichever finger it fits and mark with a pen where it stops. A jeweler can measure your finger at that mark.

6. Measure her finger while she sleeps. Wrapping string or a paper strip around a sleeping person's finger is the method everyone thinks of first, and the least reliable. String stretches, fingers swell at night, and she may wake up.

Ring Size Chart

Match your measurement to the closest row. If it falls between two sizes, choose the larger.

US size	Inside diameter	Inside circumference
4	14.9 mm	46.8 mm
4.5	15.3 mm	48.0 mm
5	15.7 mm	49.3 mm
5.5	16.1 mm	50.6 mm
6	16.5 mm	51.9 mm
6.5	16.9 mm	53.1 mm
7	17.3 mm	54.4 mm
7.5	17.7 mm	55.7 mm
8	18.1 mm	57.0 mm
8.5	18.5 mm	58.3 mm
9	19.0 mm	59.5 mm

Each full size adds about 0.8 mm to the diameter. That is roughly the thickness of a credit card, which is why a ruler alone often gives a result one size off.

What Throws the Measurement Off

The wrong hand or finger. The dominant hand is usually slightly larger, often by half a size. A ring from her right hand, or from her middle or index finger, will give a size too big for the left ring finger. Note which finger the borrowed ring comes from and tell the jeweler.

Band width. Wide bands fit tighter than narrow ones. If the ring you measured is a slim band and the engagement ring has a wide shank, go up a quarter to half a size. If you measured a wide cocktail ring, the engagement ring may need to be slightly smaller.

Temperature and time of day. Fingers are smaller in the morning and in cold weather, and larger in the evening, in heat and after exercise or salty food. A ring that fits in winter can feel tight in July. A good fit slides over the knuckle with slight resistance and sits snugly at the base without turning.

The knuckle. If her knuckles are noticeably wider than the base of her fingers, the ring must be sized to pass the knuckle. Sizing beads inside the band can then keep it from spinning.

The ring you borrowed. A ring she rarely wears may no longer fit her. Choose one you have seen on her hand recently.

If You Still Have to Guess

Sometimes there is no ring to borrow and nobody to ask. Use what you can observe.

The average women's ring size in North America is usually given as 6 to 7, and one large online jeweler lists 7 as its average. Most women fall between 5 and 8. Slim hands and a petite build point toward the lower end, taller or broader builds toward the upper end.

When in doubt, round up by half a size. A ring that is slightly loose can still be worn for the proposal and the photos. A ring that will not go over her knuckle cannot.

Three fallbacks reduce the risk further:

• Propose with a temporary setting. Some jewelers offer a simple placeholder ring so the two of you can choose the final setting and size together.

• Choose a design that resizes easily. A plain solitaire band is the most forgiving of all engagement rings.

• Confirm the resizing policy before you buy. Many jewelers include one free resize within a set period.

Resizing: Your Safety Net

Most engagement rings in gold or platinum can be resized by up to two sizes in either direction. Beyond that, the metal is strained and the stone settings can distort. The work typically takes one to two weeks and costs roughly $30 to $150, with platinum at the upper end.

Some designs leave little or no room for adjustment. Check this before you buy if you are unsure of her size.

Ring type	Can it be resized?
Plain solitaire in gold or platinum	Yes, easily
Pavé or channel-set band (stones partway around)	Limited; stones may need resetting
Full eternity band	Usually not; it must be remade
Tungsten or titanium band	No

Have the prongs and the center stone checked after any resize. If the ring fits but turns on the finger, small sizing beads inside the band tighten the fit by about a quarter size without altering the ring.