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Quite often jewelry and gemstones are measured in millimeters (mm) instead of inches since they give a more precise measurement of the size of the item. However, this may be confusing to some people as they may not be familiar with the metric system and how large a millimeter is. As a starting point it may be helpful to know that there are 25.4 millimeters in one inch. One millimeter is 1/32 of an inch. You can convert millimeters to inches by multiplying the millimeters by .03937 which will give you the equivalent in inches.
As a point of reference, a dime is 17mm or 11/16 inches, a penny is 19mm or 3/4 inches, a nickel is 21mm or 7/8 inches and a quarter is 24mm or about 1 inch. Unfortunately, eBay only allows small photos in the guides so the coins don't show up as clearly as in the original photo.
Here is a conversion chart for those who would like to use it:
1mm = 1/32 inch
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2mm = 1/16 inch
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3mm = 3/32 inch
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4mm = 1/8 inch
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5mm = 3/16 inch
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6mm = just under 1/4 inch
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7mm = just over 1/4 inch
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8mm = 5/16 inch
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9mm = just under 3/8 inch
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10 mm = just over 3/8 inch
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11mm = 7/16 inch
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12 mm = just under 1/2 inch
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13mm = just over 1/2 inch
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14mm = 9/16 inch
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15mm = just under 5/8 inch
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16mm = 5/8 inch
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17mm = just under 11/16 inch
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18mm = just under 3/4 inch
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19mm = just over 3/4 inch
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20mm = just under 13/16 inch
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21mm = just over 13/16 inch
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22mm = just under 7/8 inch
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23mm = just over 7/8 inch
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24mm = 15/16 inch
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25.4mm = 1 inch
Here is a conversion chart for those who would like to use it:
1mm = 1/32 inch
--------------------------
2mm = 1/16 inch
--------------------------
3mm = 3/32 inch
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4mm = 1/8 inch
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5mm = 3/16 inch
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6mm = just under 1/4 inch
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7mm = just over 1/4 inch
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8mm = 5/16 inch
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9mm = just under 3/8 inch
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10 mm = just over 3/8 inch
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11mm = 7/16 inch
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12 mm = just under 1/2 inch
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13mm = just over 1/2 inch
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14mm = 9/16 inch
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15mm = just under 5/8 inch
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16mm = 5/8 inch
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17mm = just under 11/16 inch
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18mm = just under 3/4 inch
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19mm = just over 3/4 inch
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20mm = just under 13/16 inch
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21mm = just over 13/16 inch
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22mm = just under 7/8 inch
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23mm = just over 7/8 inch
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24mm = 15/16 inch
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25.4mm = 1 inch
Guide created: 08/25/07 (updated 08/30/09)
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