The correlation of engineering properties and mass of ash gourd seeds was explored by using models like linear, quadratic, S-curve, power, and multivariate. The recorded range of values for seed groups (group of large mass, medium mass, and small mass) was 92.77 to 34.07 g for thousand seed mass, 28.06 to 24.46 for angle of repose, 5.64 to 4.90 m/s for terminal velocity, 213.73 to 227.12 N/mm for hardness. Coefficient of static friction was found the highest for rubber (0.488) and the lowest for aluminum (0.305) for all sizes of seeds. The recommended models based on dimensions were linear, quadratic, and power models with R 2 = 0.997 based on arithmetic mean diameter for large mass seeds, power model (R 2 = 0.999) based on geometric mean diameter for medium mass seeds, quadratic and power models with same R 2 = 0.999 based on arithmetic mean diameter for small mass seeds. The recommended area-based models for large mass, medium mass, and small mass seeds were quadratic model (R 2 = 0.997) based on projected areas perpendicular to length, power model (R 2 = 0.999) based on projected areas perpendicular to thickness, and quadratic model (R 2 = 0.999) based on projected area's perpendicular thickness, respectively. For surface area-based models, quadratic model (R 2 = 0.997) for group of large mass, quadratic and power models (R 2 = 0.999) for group of medium mass, and quadratic model (R 2 = 0.999) for group of small mass were found to be acceptable. Models based on ellipsoid volume of seed were recommended for all groups. The properties studied and models explored (best fitted) may be used for process and equipment design. Practical Applications Ash gourd seeds are discarded as waste by ash gourd processing food industries (mainly Petha industries in the northern part of India). Seeds are rich in proteins, minerals and oil, the ash gourd seed oil is high in therapeutic value, as it is rich in phytonutrients such as vitamins (A and E), squalene, terpenoids, and alkaloids. Seeds are also rich in antibacterial and antifungal properties. This makes it highly valuable for food, pharmaceutical, and cosmetic industries. The size of seed changes as the size of fruit changes and physical properties of seed depend on seed size. This study will give the knowledge of the properties of seeds, which help to design equipment for processing of seeds for various end products with the best quality. The explored models may be used for prediction of mass as per the size of seeds and help in understanding the processing operations.