Ring Sizers Compared: Which Methods Are Actually Accurate

Every sizing method will give you a number. What separates them is how much that number is worth. Some are accurate enough to order an engagement ring against, and some are only ever a rough guide. It is worth knowing which is which before you commit to a ring that cannot be altered.

Measuring a ring they already own

This is the most reliable thing you can do at home, and it beats every method of measuring a finger. A ring holds its shape, sits still and can be measured repeatedly until you are confident. Lay it flat, measure straight across the inside opening at its widest point, and you have a diameter you can convert directly.

Two cautions. Measure the same kind of ring as the one you plan to buy, because a wide band worn on that finger will be a slightly larger size than a narrow one. And make sure you know which finger it is worn on. A ring borrowed from the wrong hand can be a full size out.

A jeweller’s steel mandrel and sizing rings

This is the standard the others are measured against. A jeweller slides a set of solid metal rings onto your finger until one fits, then reads the size directly. The rings are rigid and made to a known standard, so there is nothing to stretch, flex or misread.

It also captures things a measurement cannot. The jeweller can feel whether a ring clears your knuckle, see whether it spins at the base, and try widths. For an engagement ring, an eternity band, or anything in tungsten or ceramic, this is the method to use, because those rings often cannot be resized afterwards.

Plastic reusable ring sizers

The belt-style plastic sizer that tightens around your finger is the best of the cheap options. It is rigid enough not to stretch, it passes over the knuckle so you can feel the real fit, and it costs very little.

Its weakness is the tapered tail. It is easy to pull it a notch tighter than a real ring would ever sit, which reads small. Tighten it until it feels like a ring rather than until it feels snug, and check that you can still work it back off over the joint.

Printable paper strips

A printed sizer is free and available immediately, which is genuinely useful. It is also the method with the most ways to go wrong.

The first problem is printing. If the print dialogue is set to fit to page rather than 100 percent scale, every measurement on the sheet is wrong by the same quiet percentage. Our printable ring sizer puts a bank card outline on the page for this reason: if the printed box matches a real card, the scale is right, and if it does not, nothing else on the page can be trusted.

The second problem is paper. A paper strip creases, and a creased strip pulls tighter than a ring ever would. Cut cleanly, wrap firmly rather than hard, and take the reading twice.

String, thread and dental floss

This is the method most often suggested and the least reliable. String and thread stretch, which reads small, and they bite into the finger under tension, which reads smaller still. Floss is the worst offender because it is designed to be thin and strong.

If it is genuinely all you have, use a strip of paper instead, and treat the answer as a rough indication rather than a size to order against. It is fine for narrowing down a surprise gift and not fine for an engagement ring.

On-screen sizers

A screen sizer works by first learning the physical scale of your display, usually by asking you to match an outline to a bank card, since cards are the same size worldwide. Once the screen knows its own scale, it can draw a circle at a true physical size.

Calibrated properly, this is surprisingly good, and it is the fastest option when you have a ring in your hand and nothing else. The catch is that the calibration only holds while your display does. Change the browser zoom or move to a different monitor and the scale changes underneath you, which is why our on-screen ring sizer watches for that and warns you rather than quietly showing a wrong number. Phones and tablets work best, because you can press a ring flat against the glass.

Which to use

For a ring that can be resized later, measuring an existing ring or using a plastic sizer is plenty. For an engagement ring, an eternity band or anything that cannot be altered, get sized in person and treat any home measurement as the thing you check against, not the thing you order from.

Whichever method you use, measure late in the day when your fingers are largest, and take the same measurement more than once. Once you have a number, the ring size converter will translate it into any country’s system, and the full measuring guide covers the technique in more detail.