Is there a guideline or formula for calculating the number of units (insulin- NovoLog FlexPen) per carbohydrate?

Amy Campbell


There are several ways to determine how much mealtime insulin to take to “cover” carbs. One method is to use what is known as the “1500” or “1800 Rule.” One needs to calculate the entire daily dose of insulin (both mealtime, such as NovoLog, Humalog or Apidra and basal insulin, such as Lantus or Levemir) and divide that amount into 1500 or 1800. (Whether to use 1500 or 1800 depends on the type of insulin that is used and you should ask your healthcare provider which to use.) The resulting number is a starting point for determining and fine-tuning the insulin-to-carb ratio. Another way to figure out insulin coverage for carbohydrate is to keep food records for several days, add up the carbohydrate at a particular meal, say, breakfast, and note how much mealtime insulin you took to cover those carbs (this, however, assumes that your pre- and post-meal glucose levels were within your target range). Sometimes healthcare providers will start a person off with a “1:15 ratio,” which assumes 1 unit of insulin covers 15 grams of carb. Of course, this approach can be way off for people who usually require much more or less insulin. It’s important to keep in mind that one may have a different “ratio” for each meal. If you’re interested in trying what is often called “advanced carb counting,” I’d strongly encourage you to meet with a dietitian who is well-versed in diabetes, because this level of carb counting is more of an art than a science. It requires careful and accurate carb counting (weighing/measuring foods, label reading, using carb-count books or a database), logging of both food and blood glucose, and frequent blood glucose monitoring (before and after meals) to evaluate the ratio and then fine-tune it if it’s not correct. Also, in addition to using a ratio, one needs to establish a correction or sensitivity factor which also requires frequent blood glucose checking. If all of this sounds daunting or complicated, realize that it is! Advanced carb counting really isn’t a “do it yourself” process, at least initially. Having guidance from a dietitian or diabetes educator who has experience with advanced carb counting can save you a lot of time and frustration, and help ensure that you’re being as accurate and precise as you can.

1 reply

JoleneAL 2013-04-08 10:45:35 -0500 Report

I have found that 1 unit per 50 over 140 when testing works best for me. I wouldn't have a clue what my daily insulin usage would be since it varies day to day on my activity level and food intake. As for the weighing, measuring, advanced carb counting stuff — I have a life. I would have to spend hours calcualating how much I could eat each day and then what part of the day would be left for life? Work? I really do believe sometimes people make things more complicated than they need to be.