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 & ThingsWholesale 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:

In order of increasing size…

  • 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