Since several of the designs/designers I follow come from the enlightened metric world, but I grew up with the English variant of measurements, I spend time converting. I "understand" metrics, but I think English.

Anyway, there are all manner of calculators and formula to convert a given measurement, but I found this set of charts recently that have been some handy "rules of thumb" when doing a quick read.

My thanks to Rings & Things - Wholesale Jewelry-Making Supplies for Professional Craftspeople - for putting this together... check out the entire Not too sure about millimeters? article.

If you have the inches, and need to know the millimeters:

• 1/16 inch = almost 2mm
• 1/8 inch = just barely over 3mm
• 1/4 inch = just barely over 6mm
• 3/8 inch = almost 10mm
• 1/2 inch = almost 13mm
• 5/8 inch = 16mm
• 3/4 inch = 19mm
• 7/8 inch = just barely over 22mm
• 1 inch = 25.4mm

If you have the millimeters, and need to know the inches:

• 1mm = just over 1/32 inch
• 2mm = just over 1/16 inch
• 3mm = almost 1/8 inch
• 4mm = 5/32 inch (= a bit over 1/8 inch)
• 5mm = just over 3/16 inch
• 6mm = almost 1/4 inch
• 7mm = almost 9/32 inch (= a bit over 1/4 inch)
• 8mm = 5/16 inch
• 9mm = almost 3/8 inch
• 10mm = just over 3/8 inch
• 11mm = almost 7/16 inch
• 12mm = almost 15/32 inch (= almost 1/2 inch)
• 13mm = just over 1/2 inch
• 14mm = almost 9/16 inch
• 15mm = almost 19/32 inch
• 16mm = 5/8 inch
• 17mm = almost 11/16 inch
• 18mm = just over 11/16 inch
• 19mm = 3/4 inch
• 20mm = 25/32 inch
• 21mm = just over 13/16 inch
• 22mm = almost 7/8 inch
• 23mm = 29/32 inch
• 24mm = just over 15/16 inch
• 25mm = almost 1 inch