How to measure ring size at home

Measure with a paper strip or string

This is the method jewelers Blue Nile and Brilliant Earth describe for measuring at home. Use a thin strip of paper, or a piece of string that does not stretch.

1. 1
   Wrap it at the baseWrap the strip around the base of the finger the ring is for, snug but not tight. It should sit flat, without twisting.
2. 2
   Mark the overlapMark with a fine pen where the end meets the strip. A thick mark adds error, because 1 mm of circumference is almost half a size.
3. 3
   Lay it flat and measureLay the strip flat and measure from the end to the mark in millimeters. If your ruler is in inches, multiply by 25.4.
4. 4
   Convert it to a sizeEnter the number in the ring size calculator, or convert it yourself with the steps further down this page.

GIA advises against string and paper, because string can stretch and paper can tear or curl. Treat a strip measurement as a close estimate, and confirm it with a ring sizer before you buy a ring that cannot be resized, such as tungsten, titanium or ceramic.

If you have a printer, the printable ring sizer has a strip already marked in sizes, and true-size circles to check a ring against.

Measure a ring that already fits

A ring that fits the same finger is often a better reference than a strip, because metal does not stretch. Measure straight across the inside at the widest point, from inside edge to inside edge. Measuring to the outside edge is the most common mistake, and it adds a whole size or more.

• Use a ring worn on the same finger and the same hand. Blue Nile notes that size differs with the hand you use most.
• The ring must be round inside. A bent ring, or one with a flat or shaped inner edge, gives a wrong diameter.
• A ruler is coarse for this. A 1 mm misreading of the diameter is more than a whole size, because whole sizes are only 0.8 mm apart. Calipers, or laying the ring on a printed circle chart, are more precise.
• If the ring you measured is wider than 4 mm, it already fits like a wide band. Do not add the wide band half size again if the new ring is also wide.

Convert millimeters or inches to a US ring size

US ring sizes sit on one straight-line scale. Size 0 has an inside diameter of 11.63 mm, and each whole size adds 0.8128 mm (Wikipedia's ring size table, which GIA's chart matches to within 0.05 mm). To convert by hand:

1. 1
   Get the diameterFor a strip, divide its length in millimeters by 3.1416. For a ring, use the inside diameter you measured.
2. 2
   Find the exact sizeSubtract 11.63 from the diameter, then divide by 0.8128.
3. 3
   Round upRound up to the next half size. Blue Nile and Brilliant Earth both say to choose the larger size when you fall between two. Our calculator ignores the first tenth of a size, which is smaller than a home measurement can tell apart.

When to measure your ring size

• Measure later in the day. Brilliant Earth and Blue Nile both say fingers are at their largest toward the end of the day.
• Measure at room temperature, with your hands comfortable. GIA notes that fingers shrink in the cold and swell in the heat, so a cool morning reading can be smaller than an afternoon one.
• Measure two or three times on different days. If the results differ, go with the larger one.

Knuckles and wide bands

A ring has to pass over the knuckle and still stay on at the base. GIA notes that for most people the knuckle is the widest part of the finger. If your knuckle is clearly bigger, measure both places. Blue Nile and Brilliant Earth both advise a size between the two, and the calculator does this when you enter a knuckle measurement.

Wide bands touch more of the finger and feel tighter. Brilliant Earth advises at least half a size up for bands over 4 mm. Blue Nile also suggests half a size up for wider styles, and GIA says wide bands usually need to be a bit larger.

Some jewelers suggest half a size smaller for comfort-fit bands, which are rounded inside, and others disagree. Check the brand page for the ring you want.