An image forming apparatus is adapted to distinguish a presence between a full and a partially-full toner cassette. The image forming apparatus includes a load cell positioned in a developer station. The load cell is adapted to sense a mass of a toner cassette at least during an insertion of the toner cassette into the apparatus. A processor is adapted to determine a toner volume contained in the toner cassette based on a mass differential. A controller is adapted to drive or suspend a motor in the developer station to control an operation of the image forming apparatus. The controller controls the operation based on the toner volume.