Ring sizes look simple until a customer from another country walks in. The numbers used in Hong Kong are different from those in Japan, which are different from those in the USA — and the UK uses letters instead of numbers. Jewellers cut through the confusion with one universal measurement: the inside diameter of the ring in millimetres, taken at the widest point of the finger-hole.
This guide is adapted from the JDMIS creative-drawing course book — the same material our students use before they draw a ring in actual size, because a ring drawn the wrong size becomes a ring that has to be resized at the store's cost.
Singapore follows the Hong Kong system
Singapore tends to follow the Hong Kong sizing system. That matters for two reasons: a size quoted by a local customer is an HK size, and a size quoted by an overseas customer — or an online chart — may be in US, Japanese or UK letters instead. Every size, whatever its label, corresponds to one inside-diameter measurement in millimetres, and that millimetre figure is what a designer or jeweller actually works to.
How to measure a ring size correctly
The professional tool is the ring sizer: a set of rings in full, half and sometimes quarter sizes, tried on the finger until one fits the way a finished ring should. Fit matters — a sizer worn too loose produces a ring that spins; too tight, and the finished band will not go on.
When the ring is a gift and the wearer is not available, the next best option is a ring the person already wears on the intended finger. A jeweller measures it directly on a ring stick, or measures across the widest inside diameter and converts the millimetres back to a size using a conversion chart. Whatever size a customer gives you, it is wise to check and double-check it yourself and convert it directly to the millimetre measurement.
From millimetres to a drawing
Chart measurements are written to one hundredth of a millimetre, but a drawing cannot practically be made to that precision. The course rule is simple:
- Round up to the nearest whole millimetre when the decimal is 0.50 or more (15.79 mm → 16 mm)
- Round down to the nearest whole millimetre when the decimal is 0.49 or less (15.33 mm → 15 mm)
Drawn at that rounded actual size, the design carries exactly the size the workshop needs — and the customer gets a ring that fits the first time.
Why accuracy is worth the effort
A ring not produced to scale has repercussions: the cost of enlarging or reducing it is borne by the store or the designer, and even when the customer pays nothing, they wait for the alteration or wear an uncomfortable ring. Neither is a good way to be remembered. Measuring carefully, converting to millimetres and drawing to actual size is the professional habit that prevents all of it.
Learn to draw rings to scale
Measuring is step one; drawing is where the design happens. Our guide to drawing rings to scale covers the guidelines and proportions, and the Creative Jewellery Drawing certificate course teaches the full process — top view, side view and preparation for production — in small classes in Singapore. Related reading: every type of jewellery, with pictures.
Frequently asked questions
What ring size system does Singapore use?
Singapore tends to follow the Hong Kong sizing system. Sizes quoted locally are HK sizes; overseas sizes (US, Japanese, UK letters) should be converted to the millimetre inside diameter before a ring is made.
How do you convert between ring size systems?
Through the inside diameter of the ring measured in millimetres at the widest point of the finger-hole. Every country's size corresponds to one millimetre measurement, so the millimetre figure is the common language between systems.
How can I find someone's ring size as a surprise gift?
Borrow a ring they already wear on the intended finger. A jeweller measures it on a ring stick, or measures the widest inside diameter and converts the millimetres to a size. It is the next best option after measuring the finger directly.
What tool do jewellers use to measure ring size?
A ring sizer: a set of rings in full, half and sometimes quarter sizes, tried on the finger until one fits the way the finished ring should.
Do UK ring sizes use numbers?
No - the UK uses letters instead of numbers. Hong Kong, Japan and the USA each use their own numbering, which is why jewellers convert everything to millimetres.
How precise does a ring size need to be when drawing?
Charts are written to one hundredth of a millimetre, but drawings round to whole millimetres: up when the decimal is 0.50 or more, down when it is 0.49 or less.