Yield monitoring of potato in real time during harvesting would be useful for farmers, providing instant yield and income information. In the study, potentials of candidate sensors were evaluated with different yield measurement techniques for yield monitoring system of small-sized potato harvesters. Mass-based (i.e., load cell) and volume-based (i.e., CCD camera) sensors were selected and tested under laboratory conditions. For mass-based sensing, an impact plate instrumented with load cells was placed so that the potatoes discharged from the transportation part were contacted before they fell down to the collection part. Load cell signals due to the plate bending by the impact force were calibrated to the mass of the potatoes. Effects of potato dropping height on load cell was investigated for single potato and multiple potatoes. For volume-based sensing, a CCD camera was installed above the transportation part so that the top and side images of the potatoes were captured. Area and volume were obtained from the original images and calibrated to the mass of potatoes. The calibration tests of potato showed linear calibrations with R2 of 0.98 for potatoes dropped from a height of 30 cm for the mass-based and 0.37 for volume-based approaches. This study showed potentials of candidate sensors for yield monitoring of potato yield monitoring system. Further study would be necessary to investigate the effects of vibration and harvester inclination for field application.