Instrumental testing for cotton strength requires combined measurements of tensile force and specimen mass. Because of speed requirements, High Volume Instruments (HVI) use indirect measurements of mass. Both light attenuation and air flow measurements are adjusted for errors caused by fiber fineness. The adjustment is presently made with micronaire readings which do not accurately represent the fineness for some cottons. Cut-and-weigh methods were used to compare specimen mass and fibers fineness to other fineness values. Mass errors were estimated by linear regression methods. Among 36 varieties surveyed the standard error was 6.8% for the micronaire method and 5.1% for Shirley Fineness Maturity Test fineness by the (FMT) method. Cut-and-weight fineness of fibers from the HVI strength testing zone showed a good agreement with FMT fineness values (R^® = .84).