An infusion system operable to deliver a bolus of insulin to a patient to regulate the patient's blood glucose level in respect of a current meal event comprising: an infusion device (102, 202, 402); a user interface (240, 406, 428) to receive an input qualitative meal size; a data storage element (416, 1029) to maintain historical meal data associated with historical meal events for the patient, the historical meal events being clustered into a plurality of different groups, each group of the plurality of different groups being associated with a respective qualitative meal size of a plurality of qualitative meal sizes and comprising a unique respective subset of the historical meal events assigned to the respective qualitative meal size; and a control system coupled to the infusion device (102, 202, 402), the user interface (240, 406, 428), and the data storage element (416, 1029) and configured to: a) receive an input qualitative meal size via the user interface (240, 406, 428); b) identify a patient-specific carbohydrate amount representative of a clustered subset (702, 704, 706, 708) of historical meal events corresponding to a group of the plurality of different groups that is associated with the input qualitative meal size; c) determine (906, 908, 910, 912, 914) a bolus dosage of insulin for the input qualitative meal size based at least in part on the identified patient-specific carbohydrate amount; and d) operate the infusion device (102, 202, 402) to deliver the bolus dosage of insulin to the patient. an infusion device (102, 202, 402); a user interface (240, 406, 428) to receive an input qualitative meal size; a data storage element (416, 1029) to maintain historical meal data associated with historical meal events for the patient, the historical meal events being clustered into a plurality of different groups, each group of the plurality of different groups being associated with a respective qualitative meal size of a plurality of qualitative meal sizes and comprising a unique respective subset of the historical meal events assigned to the respective qualitative meal size; and a control system coupled to the infusion device (102, 202, 402), the user interface (240, 406, 428), and the data storage element (416, 1029) and configured to: a) receive an input qualitative meal size via the user interface (240, 406, 428); b) identify a patient-specific carbohydrate amount representative of a clustered subset (702, 704, 706, 708) of historical meal events corresponding to a group of the plurality of different groups that is associated with the input qualitative meal size; c) determine (906, 908, 910, 912, 914) a bolus dosage of insulin for the input qualitative meal size based at least in part on the identified patient-specific carbohydrate amount; and d) operate the infusion device (102, 202, 402) to deliver the bolus dosage of insulin to the patient. a) receive an input qualitative meal size via the user interface (240, 406, 428); b) identify a patient-specific carbohydrate amount representative of a clustered subset (702, 704, 706, 708) of historical meal events corresponding to a group of the plurality of different groups that is associated with the input qualitative meal size; c) determine (906, 908, 910, 912, 914) a bolus dosage of insulin for the input qualitative meal size based at least in part on the identified patient-specific carbohydrate amount; and d) operate the infusion device (102, 202, 402) to deliver the bolus dosage of insulin to the patient.