Determining the right width, or diameter, of rope can be a safety issue, especially if you plan to use the rope to secure one of your projects. Take quick and accurate measurements of any rope with a pair of calipers, but use at least four measurements of the rope's diameter and average them to ensure an accurate measurement.
Taking a Measurement
Place the rope in the caliper's jaws and close the jaws until they fit snugly against the edges of the rope. Rope diameter is measured from one of the strands of the rope to the strand on the opposite side. When measuring, the jaws of the calipers should each touch only one strand. If your calipers touch multiple strands, your measurement will be too small.
Take Your Measurements
Caliper measurements are taken in whole and hundredth units. Whole units are counted by the marks on the scale to the left of the zero. Hundredths are counted by the number of marks to the left of the main mark on the hundredths scale. The measurement lines up with a mark on the scale on the main body of the calipers. This number, multiplied by two, is the measurement of the hundredths units of the rope's width.
For example, if you are measuring in millimeters and count 12 marks on the main scale and 7 on the hundredths scale, your rope has a width of 12 millimeters plus 0.14 millimeter, or 12.14 millimeters. Note that some calipers use a digital readout, which displays the units of width based on the position of the caliper's jaws.