Ring Sizing
Here are some charts to help you when working on glass rings. Remember to add in the thickness of the bead release.

Diameter: a straight line passing through the center of a circle or sphere and meeting the circumference or surface at each end.

Circumference: the outer boundary of a circular .

Mandrel	Diameter
in inches	without release
3/8	0.38
7/16	0.44
1/2	0.50
9/16	0.56
5/8	0.63
11/16	0.69
3/4	0.75

The Mandrel estimates below are ESTIMATES ONLY, based on size. you will need to test out your release layers for better sizing.

Ring Size	Diameter		Circumference		Mandrel
US Standard	Inches	MM	Inches	MM	Estimate
5	0.618	15.7	1.94	49.3	9/16
5 1/2	0.634	16.1	1.99	50.6	9/16
6	0.650	16.5	2.04	51.8	9/16
6 1/2	0.666	16.9	2.09	53.1	5/8
7	0.682	17.3	2.14	54.4	5/8
7 1/2	0.698	17.7	2.19	55.7	5/8
8	0.714	18.1	2.24	56.9	11/16
8 1/2	0.730	18.5	2.29	58.2	11/16
9	0.746	18.9	2.34	59.5	11/16
9 1/2	0.762	19.4	2.39	60.8	11/16
10	0.778	19.8	2.44	62.1	11/16
10 1/2	0.794	20.2	2.49	63.3	3/4
11	0.810	20.6	2.54	64.6	3/4
11 1/2	0.826	21.0	2.59	65.9	3/4
12	0.842	21.4	2.64	67.2	3/4