Inside Ring Blank Measurements for Calculating Ring Blanks

Nancy LT Hamilton

Last updated:  11/7/21

Formula:  The formula for determining ring blank lengths adjusts for the compression that occurs on the inside of the ring and the stretching that occurs on the outside of the ring.  Knowing the inside measurement for the size of the ring is essential for this method.  Interior diameter (in millimeters) + the metal thickness (also in millimeters) X 3.145.  This should work unless you need to square up those edges in a miter cutting vise.  Add .25 or .50 mm extra – depending on how off your edges are – to account for this metal loss.  Here’s an example of the formula for an 8.5 sized ring made from 18 gauge metal.  ID 18.4 + Metal thickness 1 mm X 3.145 = 61 mm.