Mass flow measurement of pneumatically conveyed cotton is important in at least two processes: yield monitoring during harvesting, and input and output determinations at various stages of ginning. In this work, two electronic devices were constructed and tested for measuring the flow of pneumatically conveyed cotton. One (device A) was used to collect data in the seed-cotton unloading duct of a gin, a cotton picker duct, and a lint-cleaner-exhaust duct. The other (device B) was used to collect data in the seed-cotton unloading duct of a gin and a lint-cleaner-exhaust duct. Tests were conducted in which known amounts of cotton were conveyed through the duct over a known time period, making it possible to calculate the average actual material flow rate. The average output of each device during the test runs was also calculated. Actual flow rate was compared to measured flow rate with linear regression. For seed cotton in the unloading duct, both devices performed well. For seed cotton in the picker chute, device A performed well, but device B was not tested. For waste in the lint-cleaner-exhaust duct, device A performed well and better than device B. In most cases, the correlation between sensor output and cotton mass flow was strong. Both devices look promising for application in appropriate locations in a cotton picker or gin.