We are often called out to a job-site or facility to assist in determining the size of wire rope (and are happy to do so!). To measure yourself, the actual diameter of a wire rope is the diameter of a circumscribed circle that will enclose all the strands. It’s the largest cross-sectional measurement as shown here. You should make the measurement carefully with calipers, preferably digital. The illustrations above show the correct and incorrect methods of measuring wire ropes with even numbers of outer strands.
It should be mentioned that wire rope is normally made slightly larger than its catalog (or nominal) size. Wire rope allowable tolerances are +8% on rope sizes up to 1/8”, +7% on sizes between 1/8” and 3/16”, +6% on sizes between 3/16” and 5/16” and +5% on wire rope sizes over 5/16”. Ropes will also lengthen during use and the diameter will get slightly smaller over time so please keep that in mind while measuring. Additionally, wire rope running over sheaves will flatten the strands and alter the diameter over time.
It can therefore be tricky to determine the exact size and type of wire rope! It is best to find your manual, original documentation or Google it (just kidding!) We at Fulcrum lifting are a FULL SERVICE RIGGING SHOP and are happy to assist – so call your rep or bring in a sample and we can help in getting you the correct replacement.