I like to measure the actual string that is on the bow for best fit.Bows are different,I have 3-64" bows and each one is a different length.I have a 21st Century Edge that is 66" but when I measure it ntn it is 64"ntn but my string on it is 62&3/8" and that gives me a 6&3/4" brace.Thats why I prefer to measure the actual string length on the individual bow.The -3 for longbow and -4 for recurves is a good general rule but does not always work when the string is missing,but measure the string.