Determining your strap size in 3 Easy Steps:
#1 - Use a standard ruler that offers a Centimeter side. Always measure in Centimeters as Inches are too large for an accurate conversion to Millimeters.
#2 - Measure the space between your watches lugs. (see red line labeled "Inner Space" in image)
#3 - Once you have the measurement in Centimeters, move the decimal one place to the right to convert your measurement into Millimeters.