This insulin to carb ratio calculator computes the number of carbohydrate grams disposed of by one unit of insulin from the prescribed diabetes treatment. Below the form you can find instructions about both tabs and about counting carbs and insulin units.

Carbohydrate intake in grams:*
Number of daily insulin units:*
Carbohydrate intake in grams:*
Insulin to Carb Ratio 1:X where X is:*

How does the insulin to carb ratio calculator work?

This is a health tool that computes the I:C ratio as well as due insulin units in specific cases. There are two tabs available for usage:

■ The first focuses on the transformation from grams of carbohydrate intake in I:C ratio based on the number of insulin units prescribed. All the user needs to do is fill in the two fields and will be given the accurate ratio.

■ The second tab in the insulin to carb ratio calculator helps the user account for the necessary number of insulin units due after a specific meal/ intake of carbs. By knowing the amount of CHO and the insulin ratio in the treatment plan, the results shows the required units.

While medical providers prescribe a personalized insulin dose regimen, this is still a standardized chart therefore needs to be adapted to lifestyle changes and patients find themselves in need to calculate certain insulin doses.

The ICR is defined as the number of grams of carbohydrate that are covered/ disposed of by 1 insulin unit. These ratios are used either to adapt dosage to lifestyle and diet or even to restrict blood glucose to target levels.

Insulin dosage guidelines

The main focus is on how much bolus insulin should be taken considering meals and snacks or when there is need to correct high blood sugar levels.

The daily dosage can be divided in two approximately equal portions:

■ The constant one – also called basal insulin replacement, is used to replace insulin overnight during fasting (between meals).

■ The other dose, which is highly customizable, is used for carbohydrate coverage and to correct abnormal blood sugar. This part is prescribed as insulin to carbohydrate ratio.

There are several approaches in dosage prescribed:

■ Fixed dosage – with different units per meal, usually depending on personal factors, sensitivity and moment of the day.

■ Sliding scale of insulin – based on blood levels, the higher, the greater the insulin injection. This method has improved control but requires constant monitoring.

■ Carb counting – with adaptation of fixed dosage or sliding scale. This will be described below.

Factors influencing the sensitivity of the response to insulin vary from patient to patient, vary by the time of the day but also with physical activity and others. Sensitivity is quantified by the high blood sugar correction. For instance some patients require larger doses in the morning than lower as the day progresses.

In most commercial insulin products, one unit disposes of 12 to 15 grams of carbs, suggesting a 1:12 or 1:15 I:C. However, the range is wider than this, almost varying between 4 and 30 grams.

These are often adapted because of individual insulin sensitivity factor that might require different strengths.

A dose of insulin with 1:10 results in larger doses than a ratio of 1:15.

One unit of insulin usually drops blood sugar levels by 50 mg/dL.

Rapid acting insulin aims to regulate the heightened levels and is more effective than slow action insulin. I:C ratio is used to delimitate between the effects of the two types and to clarify exactly the number of carbohydrate grams that are covered by one unit of insulin.

Carbohydrate coverage for meals (CHO insulin dose) = total grams of CHO divided by the number of CHO disposed by 1 insulin unit.

Result appears as insulin: CHO ratio. For example, after a meal consisting of 70 grams of carbohydrates, a patient with a insulin to carb ratio of 1:10 should require 7 units to regulate blood sugar.

High blood sugar correction = (Actual blood sugar – Target blood sugar ) / Correction factor.

Total mealtime dose = CHO insulin dose + High blood sugar correction.

Carbohydrate counting

Carb counting is used by type 1 diabetes patients on the basal bolus insulin regimen as a mean of managing blood glucose levels and of dosing insulin to match their intake.

Dietary carbohydrates include sugars, starches and fiber but usually only the first two are counted in as raising blood glucose levels. Carbohydrates are either counted in grams or portions (a portion equals 10g) and sometimes the glycemic index of the product is analyzed as well.

Before starting to count carbs most people wonder where they will be able to get this information from for each meal. There are several means of information:

■ Food labels – paying attention to whether these are labeled by serving or per 100 grams of product and then calculating the individual portion;

■ Reference lists;

■ Nutritional information;

■ Online recipe information for restaurants.

This method is either based on counting and comparing to a target amount or on a less accurate but faster visual approach where approximately ¼ or ⅓ of the plate is reserved for carbs.

The 500 rule

The rule in question is based on the assumption that an average daily carbohydrate intake is of about 500 grams. By dividing this to the number of average prescribed insulin units, results a ratio which suggests the amount of carbohydrate grams disposed of by each insulin unit in the treatment plan.

Example: for a patient taking 25 units of insulin per day the I:C ratio or ICR is 500/25 = 1:20.

The following table exemplifies the average insulin units in different plans and their corresponding ratios based on the 500 approach:

Insulin dosage I:C
8 - 11 1:50
12 - 14 1:40
15 - 18 1:30
19 - 21 1:25
22 - 27 1:20
28 - 35 1:15
36 - 45 1:12
46 - 55 1:10
56 - 65 1:08
66 - 80 1:06
81 - 120 1:05
> 120 1:04


1) Bergenstal RM, Johnson M, Powers MA, Wynne A, Vlajnic A, Hollander P, Rendell M. (2008) Adjust to target in type 2 diabetes: comparison of a simple algorithm with carbohydrate counting for adjustment of mealtime insulin glulisine. Diabetes Care; 31(7):1305-10.

2) Mendosa: Insulin-to-Carb Ratios Made Easy; Gary Scheiner, MS, CDE; October 17 2015.

3) Cresswell P, Krebs J, Gilmour J, Hanna A, Parry-Strong A. (2015) From 'pleasure to chemistry': the experience of carbohydrate counting with and without carbohydrate restriction for people with Type 1 diabetes. J Prim Health Care; 7(4):291-8.

13 Jan, 2016