How do I measure rigging wire diameter and length?

Diameter is measured across the outside of the strand bundle, and a worn or corroded section will read differently from a sound one. Take several readings along the length and use the consistent figure rather than the smallest.

Length is where errors are expensive. The measurement that matters is pin-to-pin: the distance between the centres of the load-bearing holes at each end, with the turnbuckle at mid-adjustment. Measuring a wire lying on the ground without accounting for fitting geometry produces stays that will not fit.

Set turnbuckles to roughly half their travel before measuring. That leaves adjustment in both directions for tuning and for future settling. A wire measured with the turnbuckle fully open has nowhere to go.

For anything structural, have the rigger measure. Most riggers will not warrant wire made to an owner’s measurements, and a mismeasured stay is an expensive lesson. Use your own measurements for budgeting and for checking a quote, not for ordering.