How to Measure Your Wrist for a Tennis Bracelet Fit

Wrap a soft measuring tape or a strip of paper snugly around your wrist, just past the bone on the little-finger side, and read the number in millimetres. Then add slack for the fit you want: roughly 10 to 13 mm for a bracelet that barely moves, 14 to 19 mm for a normal fit, 20 to 25 mm if you want it to drape. Measure the wrist you will actually wear it on, at the end of the day when your hands are at their largest.

That is the whole method. The rest of this guide is about the parts that go wrong: where the tape sits, why bracelet "sizes" are not standardised the way ring sizes are, and how the diamonds themselves change how much length you need.

Where to put the tape

Feel for the small knob on the outside of your wrist below the little finger. That is the head of the ulna, and a tennis bracelet naturally settles just below it, on the hand side, because the bone stops it sliding further. Put the tape there, not up the forearm, and keep it perpendicular to the arm rather than angled.

Two details matter more than people expect:

• Snug, not tight. The tape should sit against the skin without denting it. If you can see a groove when you take it off, you have pulled 2 to 3 mm out of your own measurement.
• Same wrist, same time. Wrists differ left to right, and most people measure 2 to 4 mm larger in the evening, in heat, or after exercise. A bracelet sized on a cold morning measurement will feel tight most of the time.

Record the number in millimetres. Inches force you to round to the nearest eighth, which is 3.2 mm, and 3 mm is the difference between a bracelet that stays put and one that spins.

Bracelet length is not a standard size

Ring sizing has an actual international standard behind it. ISO/TC 174, the ISO committee for jewellery, publishes ISO 8653:2016, Jewellery — Ring-sizes — Definition, measurement and designation, second edition dated 15 January 2016, which defines how ring size is measured and designated so that a size means the same thing from one workshop to the next. Its scope covers rings. There is no equivalent published standard for bracelet lengths.

The practical consequence: "size 7" on a bracelet is a house convention, not a specification. Some makers quote the finished inside length including the clasp, some quote the diamond line only, and some quote your wrist size and add their own allowance. Always give and ask for a number in millimetres, and ask whether it includes the clasp.

Three ways to measure, ranked

1. Soft dressmaker's tape. The most accurate home method. Read the millimetre mark where the tape overlaps, take three separate measurements, and use the middle one.
2. Paper strip and a ruler. Cut a strip about 10 mm wide from printer paper or a receipt, wrap it, mark the overlap with a pen, lay it flat and measure to the mark. Accurate to about a millimetre, which is all you need.
3. Measure a bracelet you already like. Lay it flat and fully extended, clasp closed, and measure the inside length from one end of the interior to the other. This is the single best input if the existing bracelet fits the way you want, because it removes the guesswork about slack entirely.

Do not use string or a shoelace. Both stretch under tension, and the error runs in the direction that makes the finished bracelet too big. Do not buy a laser measuring gadget or a wrist gauge either. A paper strip lands within a millimetre of a jeweller's tape, and a millimetre is well inside the adjustment range of a single link.

How much slack to add

The slack you add is a wearing preference, not a fitting rule. Here is how the three common choices behave, worked through for a 160 mm wrist:

For a standard fit, adding 16 mm gets you close:

• 140 mm wrist to about 156 mm (6.1 in)
• 150 mm wrist to about 166 mm (6.5 in)
• 160 mm wrist to about 176 mm (6.9 in)
• 170 mm wrist to about 186 mm (7.3 in)
• 180 mm wrist to about 196 mm (7.7 in)

Commonly stocked lengths are 7 in (177.8 mm) and 7.5 in (190.5 mm), which is why so many wrists end up in a bracelet that is 5 to 10 mm off. If your number sits between stock lengths, a custom length is one of the few upgrades in fine jewellery that is worth paying for, because it fixes the only problem a tennis bracelet reliably has.

The diamonds change the number

A tennis bracelet is a line of rigid links, so it does not follow the wrist as closely as a chain. The bigger the stones, the longer and stiffer each link, and the more the bracelet behaves like a polygon rather than a circle. On a wide bracelet, add 2 to 3 mm over what you would choose for a thin one at the same wrist, because the interior of a thick setting takes up space your wrist has to share.

Length and carat weight are linked directly. HRD Antwerp, one of the grading laboratories, states on its 4Cs page that "one carat equals 0.2 grams or 100 points, which indicates the weight." Add 15 mm of length at a fixed stone size and you are adding several more stones, so the total carat weight and the price both rise. Ask for the price at your actual length rather than the advertised length, and see our other guides if you are still deciding on stone size.

One honest caveat about grading. HRD describes clarity as reflecting "the size, number and location of these characteristics when examined with a 10x loupe," and colour as "determined by comparison with a series of master stones." Those procedures apply to individually graded stones. The small diamonds in most tennis bracelets are not sent for individual reports, so a claim like "F-G colour, VS clarity" on a bracelet is the maker's own assessment of a parcel, not a laboratory grade. Judge it in person, or ask what the tolerance is across the line.

Adjustment and the marks on the clasp

Length changes happen in whole links, usually 3 to 5 mm each, so the final fit lands within a few millimetres of your target rather than exactly on it. Ask for removed links to be returned to you, and check the quality marks survive the work. In Canada, marking is voluntary: the Competition Bureau's Guide to the Precious Metals Marking Act and Regulations states that "it is not mandatory to mark or advertise a precious metal article for quality," but when a quality mark is applied the article must also bear a trade-mark applied for or registered in Canada. The Precious Metals Marking Regulations add that the trade-mark must be applied by the same method as the quality mark. Those marks are often on the clasp or the end link, which is exactly the part a shortening touches.

What a measurement cannot settle

Your wrist cross-section is oval, not round, and a flat wrist wears a bracelet slightly looser than a round wrist of the same circumference. Nothing you measure at home captures that, which is why a snug fit is a small gamble and the standard allowance is the safe answer if you are buying as a gift.

Currency is the other thing that moves. American charts quote inches and US dollars. As of 17 August 2026, the Bank of Canada daily rate was 1.3865 CAD per US dollar, so a US price is close to 39% higher in Canadian dollars before duty and tax. Compare CAD to CAD.

What to do next

Measure your wrist tonight, write the millimetre figure down, and pick your fit from the table above. Send your jeweller four things: wrist measurement in millimetres, fit preference, stone size or total carat weight, and metal. If you are working on a ring at the same time, our loose diamond search and engagement ring settings let you match stone quality across both pieces, and the finishing step is where metal, size and engraving get confirmed before anything is made.

Sources

• International Organization for Standardization, ISO 8653:2016, Jewellery — Ring-sizes — Definition, measurement and designation, second edition, 2016. Preview read at cdn.standards.iteh.ai.
• HRD Antwerp, 4Cs, hrdantwerp.com/4cs, accessed 18 August 2026.
• Competition Bureau Canada, Guide to the Precious Metals Marking Act and Regulations, competition-bureau.canada.ca, accessed 18 August 2026.
• Government of Canada, Precious Metals Marking Regulations (C.R.C., c. 1303), laws-lois.justice.gc.ca, accessed 18 August 2026.
• Bank of Canada, Daily exchange rates, USD/CAD (FXUSDCAD), observation for 17 August 2026, bankofcanada.ca.