Instrument testing of cotton strength requires a combined measurement of tensile force and specimen mass. High Volume Instruments (HVI) use indirect methods (light attenuation and air pressure) to estimate mass. Cut-and-weigh methods were used to survey the precision and accuracy of bundle mass used to measure strength in 15 HVI systems. A large mass level difference between HVI models from different vendors was observed but it did not appear to adversely affect the strength. However, cottons very high or very low in micronaire gave large differences in both mass and strength. New micronaire correction equations were developed to reduce HVI strength errors.