A method implemented in a wireless communication system including a wireless transmit/receive unit (WTRU), a Node-B and a radio network controller (RNC) for quantizing multiplexed data allowed by grants to closely match a selected enhanced uplink transport format combination (E-TFC) transport block size is disclosed. The amount of scheduled and non-scheduled data allowed to be transmitted is quantized so that the amount of data multiplexed into an enhanced uplink (EU) medium access control (MAC-e) protocol data unit (PDU) more closely matches the selected E-TFC transport block size. In an embodiment, the amount of buffered data allowed to be multiplexed by at least one grant, (a serving grant and/or a non-serving grant), is quantized so that the sum of scheduled and non-scheduled data including MAC header and control information multiplexed into a MAC-e PDU more closely matches the selected E-TFC transport block size.