It's quite common to see the size of jewelry pieces in millimeters (MM), although many people want to know the size in inches. If you would like to know inches instead of millimeters, a straightforward formula can help you figure it out:

Simply take the number of millimeters and divide by 25.4. You will then get a decimal that can be converted to an inch. Example: 40 millimeters is approximately 1.6 inches, calculated as 40 / 25.4 = 1.57 inch.

The following chart demonstrates common conversions for easy reference:

		Millimeters		Inches
		1 Millimeter		0.04 Inches
		2 Millimeters		0.08 Inches
		3 Millimeters		0.12 Inches
		4 Millimeters		0.16 Inches
		5 Millimeters		0.20 Inches
		6 Millimeters		0.24 Inches
		7 Millimeters		0.28 Inches
		8 Millimeters		0.31 Inches
		9 Millimeters		0.35 Inches
		10 Millimeters		0.39 Inches
		11 Millimeters		0.43 Inches
		12 Millimeters		0.47 Inches
		13 Millimeters		0.51 Inches
		14 Millimeters		0.55 Inches
		15 Millimeters		0.59 Inches
		16 Millimeters		0.63 Inches
		17 Millimeters		0.67 Inches
		18 Millimeters		0.71 Inches
		19 Millimeters		0.75 Inches
		20 Millimeters		0.79 Inches
		21 Millimeters		0.83 Inches
		22 Millimeters		0.87 Inches
		23 Millimeters		0.91 Inches
		24 Millimeters		0.94 Inches
		25 Millimeters		0.98 Inches
		26 Millimeters		1.02 Inches
		27 Millimeters		1.06 Inches
		28 Millimeters		1.10 Inches
		29 Millimeters		1.14 Inches
		30 Millimeters		1.18 Inches
		31 Millimeters		1.22 Inches
		32 Millimeters		1.26 Inches
		33 Millimeters		1.30 Inches
		34 Millimeters		1.34 Inches
		35 Millimeters		1.38 Inches
		36 Millimeters		1.42 Inches
		37 Millimeters		1.46 Inches
		38 Millimeters		1.50 Inches
		39 Millimeters		1.54 Inches
		40 Millimeters		1.57 Inches