A smart locker system includes an enclosure unit and a cassette unit. The smart locker is extendable by adding additional enclosure units and the cassette units. The cassette unit includes storage bins and a control bin. The cassette unit contains different size of storage bins and a control bin. The smart locker system further includes a touch screen and authentication devices. The smart locker system can arrange the storage bins and the control bins to maintain the height of the smart locker system.