Metric Ruler for determining inches versus millimeters
(ruler shown actual size)

This is great for determining jump ring and split ring size, also bead sizes, simply by looking at the top and comparing to the bottom row.

Examples:
6mm bead------------------1/4"
12mm jump ring-----------1/2"
 

Approximate Measurement Conversion Chart also try: WORLD WIDE METRIC for more options!

Millimeters to Inches Conversion Chart 1 inch = 25.4mm Size in mm Closest equivalent in Inches 1mm just over 1/32 of an inch 2mm just over 1/16 of an inch 3mm 1/8 of an inch 4mm 5/32 of an inch 5mm 3/16 of an inch 6mm 1/4 of an inch 7mm 9/32 of an inch 8mm 5/16 of an inch 9mm 11/32 of an inch 10mm 3/8 of an inch 11mm 7/16 of an inch 12mm 15/32 of an inch 13mm 1/2 of an inch 14mm 9/16 of an inch 15mm 19/32 of an inch 16mm 10/16 of an inch 17mm 11/16 of an inch 18mm 23/32 of an inch 19mm 3/4 of an inch 20mm 13/16 of an inch 25mm 15/16 of an inch 1mm = 1/32" 8mm = 5/16" 2mm = 1/16" 9mm = almost 3/8" 3mm = 1/8" 10mm = 5/16" 4mm = 5/32" 11mm = 7/16" 5mm = 3/16" 12mm = almost 1/2" 6mm = almost 1/4" 20mm = almost 13/16" 7mm = almost 1/4" 25mm = almost 1" Inches to MM: (in * 25.4) 1/8" = 4mm 1/2" = 12.5mm 1/4" = 6.5mm 1" = 25.4mm Grams to Pounds: (g * 0.002205) 1g = 0.0022 lb 5g = 0.01 lb 100g = 0.22 lb 453.6g = 1 lb 500g = 1.10 lbs 1 Kg = 2.2046 lbs Ounces to Pounds 1oz = 0.625 lb 8 oz = 1/2 lb 16 oz= 1 lb   Other Measurements 1 Troy oz = 31g 1 Avoirdupois oz = 28g

Wire Gauge

Wire gauge is best remembered  in wire thickness or gauge: The larger the number, the smaller the diameter of the wire.

Gauge Inches Millimeters 10 0.102 2.59 11 0.091 2.31 12 0.081 2.06 13 0.072 1.83 14 0.064 1.63 15 0.057 1.45 16 0.052 1.32 17 0.045 1.14 18 0.04 1.02 19 0.036 0.91 20 0.032 0.81 21 0.028 0.71 22 0.025 0.64 23 0.023 0.58 24 0.02 0.51 25 0.0179 0.455 26 0.0159 0.404 27 0.0142 0.361 28 0.0126 0.32 29 0.0113 0.287 30 0.01 0.25 31 0.0089 0.226 32 0.008 0.2 33 0.0071 0.18 34 0.0063 0.16 35 0.0056 0.142 36 0.005 0.13 37 0.0045 0.114 38 0.004 0.1