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Carb to Insulin Ratio
Calculations of carb to insulin ratios for Type 1 Diabetes

A carbohydrate to insulin ratio is the amount of insulin used to lower the blood sugar from a particular amount of grams of carbohydrates eaten. For example, some people have a 15:1 carbohydrate-to-insulin ratio or they take 1 unit of insulin for every 15 grams of carbohydrates they eat. But other Type 1s need 1 unit of insulin for every 10 or even 8 grams of carbohydrates. Every person responds a little differently to insulin.

The 450/500 rule goes as follows:

If a person is taking rapid-acting insulin such as Humalog, Novolog or Apidra they would follow the 500 rule which states:

Divide 500 by the total daily dose of insulin. The result is the grams of carbohydrates that are approximately covered by 1 unit of insulin. For example, add up all the insulin you take for the day and divide by 500. If your total daily dose was 45 units, you would divide 500 by 45 and your ratio would be 11:1.

If a person is taking short-acting insulin such as Humulin R or Novolin R (Regular insulins) they would follow the 450 rule which states:

Divide 450 by the total daily dose of insulin. The result is the grams of carbohydrates that are approximately covered by 1 unit of insulin. For example, add up all the insulin you take for the day and divide by 450. If your total daily dose was 45 units, you would divide 450 by 45 and your ratio would be 10:1.

http://www.insulin-pumpers.org/howto/ratio.cgi (calculator)
http://www.bddiabetes.com/US/main.aspx?cat=1&id=303 (chart)

Marci Sloane, MS, RD, LD/N, CDE, is a registered and licensed dietitian/nutritionist and certified diabetes educator with a degree in Nutrition and Physiology from Teachers College at Columbia University. Marci is the author of The Diet Game: Playing for Life! More about Marci Sloane

The goal of Destination Diabetes is to be a useful and credible resource for the more than 20 million children and adults who have diabetes in the U.S. and their families. Destination Diabetes provides information on a wide range of diabetes health and wellness topics. Articles are written or reviewed by diabetes advisors who have experience in diabetes education.