An insulin-to-carb ratio tells you how much rapid acting insulin you need to cover a specific amount of carbohydrate. This allows you to dose your insulin based on the amount of carbohydrate that you eat at a meal.

The insulin sensitivity factor tells you how many points, in mg/dL or mm/oL, your blood sugar will drop for each unit of insulin that you take. The insulin sensitivity factor is also sometimes called a “correction factor.” You need to know this number to correct a blood sugar level that’s too high.