How to Measure Wire Rope Diameter Correctly

The most common mistake when replacing a rope or building a new system is measuring the rope diameter incorrectly. The wrong diameter means a rope that does not fit the sheave grooves, slips in the clips or is weaker than required. Fortunately, a caliper and a few simple rules are enough for a correct measurement.

Rule 1: Measure across the strand crowns

The cross-section of a wire rope is not a perfect circle; the strands form crowns on the outside. Place the caliper jaws on the outermost points of two opposite strands. If you place the jaws in the valley between two strands, the reading will be smaller than the true value. A caliper with wide jaws makes the job easier.

Rule 2: Measure at three different points

Take readings at three points at least 1 metre apart along the rope, in two perpendicular directions at each point. Use the average as the rope diameter. On used ropes, if one reading is clearly smaller, there may be internal wear or core damage in that area and the rope may need to be replaced.

Rule 3: Tolerance is normal on new rope

New wire ropes are manufactured slightly above the nominal diameter (standards define a positive tolerance). As the rope works under load, its diameter settles a little. So a new rope measuring slightly thicker than nominal is nothing to worry about.

What information should you give for a replacement rope?

• Measured diameter (mm)
• Construction (e.g. 6x19, 7x7) — you can count the strands and wires
• Core type: fibre (FC) or steel (IWRC)
• Finish: galvanized, stainless or lubricated/black
• Required length and end terminations

Simply send this information with a photo via WhatsApp and our team will identify the right equivalent. For the meaning of construction codes, see our wire rope guide.