A fluid flow tester for measuring minute volumes of fluid and for calibrating medical devices, such as intravenous infusion pumps, includes a plurality of valves and associated conduits which direct fluid from the device being tested to a transparent vertical column. A plurality of sensors, each including a light emitting diode and a light detector, are arranged along the axial length of the column at a predetermined spacing between adjacent sensors. Fluid from the device being tested is directed through the flow tester by the valves and associated conduits into the column where it rises. The meniscus of the fluid rising in the column is detected by the sensors. The sensors provide signals to a microcontroller which calculates the time that it takes for the fluid to pass each sensor. Knowing this timing and the volume of the column, the flow rate of the fluid may be calculated by the microcontroller.