Intro to Carb Calculation By Examples

Faisal Parwani
4 min readApr 19, 2024

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People with Diabetes Type 1 need to inject insulin depending on amount of carbs they are eating. Food we eat is mainly consist of Carbohydrates, Fats , Protein etc. Sugar e.g. is 100% carbohybrades means if you eat 10 grams of sugar then you are taking 10 gram of Carbs.

Its not only sugar that will increase your blood glucose level, its Carbohydrates. If you are consuming rice, potatoes, fruits, corn, white or wheat flours, milk, yoghurt, etc. You need to calculate the amount of carbs. You inject certain amount of insulin based on amount of carbs you are eating.cted.

Here in this article we will focus on calculating the total amount of carbs in your meal.

Disclaimer!!! Amount of insulin calculation (that you will inject) is different for every one. “Carbs to Insulin Ratio” is different for every one. Should be initially done in consultation with Experts/Doctors and later you will learn and adjust your self.

Where is the Magic

The amount of carbohydrate found in 1 gram of a food is called “Carb Factor”. Only hard part for carb calculation is to know the Carb factor of items you are using in a recipe such as Banana, Apple, Milk, Orange Juice, oranges, Wheat flour, Rice etc. You can learn it from different websites, Mobile Apps etc. Once you know the magic number , its simple math to calculate carbs in any meal.

Example 1 : One glass of Milk.

If you are drinking a single glass (say 200 ml) of milk, you can easily calculate the carbs if you know how much carbs are in 1 ml. if we take an example of Milk , you can see on package that 100 ml of Milk consist of roughly 4.7 carbs. So doing simple math

if 100 ml Milk = 4.7 gm carbs

it implies that => 1 ml Milk = 4.7 / 100 = 0.047 gm carbs (This is Milk’s Carb Factor)

and 200 ml milk = 0.047 x 200 = 9.4 gm of carbs.

You can use similar calculation when eating individual substance such as any fruit, nuts, milk, etc. Only thing you need to know/calculate is to get the magic number i.e carb factor i.e amount of carbs in 1 gm of that item. Once you have carb factor you can multiply it with amount of item and calculate total carbs that you are consuming.

Example 2 : How to calculate Carbs in Banana Shake

Its the simplest recipe that i can think of where we have more than one ingredient : Milk and Bananas (Yes don’t need to add additional sugar)

Carbs in 100 gm Banana = 21 gm

Carb Factor of Banana => means 1 gm banana = 21 / 100 = 0.21 gm

100 ml Milk: 4.5 gm

means => 1 ml Milk : 4.5 / 100 = 0.045 gm

So our Carb factor for this recipe are

1 gm Banana = 0.21 gm

1 ml Milk = 0.045 gm

you can add your own ratio of Milk and banana to make shake, only thing to remember how much banana and milk are used. Lets say if i use

4 Bananas (say weight = 300 gm) => implies 300 x 0.21 = 63 gm Carbs

1 Liter Milk => implies 1000 x 0.045 = 45 gm Carbs

Total Milk shake Weight = (300 + 1000) = 1300 gm

Total Milk shake Carbs = 63 + 45 = 108 gm

So 1300 gm Milkshake contains 108 gm (carbs)

Which means :

Milk shake carb factor is : 1 gm Milkshake =108 / 1300 gm = 0.083 Carbs.

Above will be your formula for Milk Shake.

If you drink 200 ml of this Milk shake , it is equal to : 200 x 0.083 = 16.6 carbs. you need to give insulin for this 16.6 gm. (Using the ratio you learn from Doctor).

Example 3: Carb calculation for Home made whole wheat Bread (Roti)

Ingredients to make dough:

Wheat Flour : 300 gm.

Water: 190 gm

Salt: to taste.

Only thing with carbs in our this recipe is Wheat flour. We know from the package that 100 gm of Wheat flour contains 65 gm of Carbs thus we have the carb factor : 1 gm wheat flour = 65 / 100 = 0.65 carbs.

we used 300 gm flour so

Total carbs in 300 gm wheat flour = 300 x 0.65 = 195 gm carbs.

Thus we can conclude that

Total weight of dough (190 gm water + 300 gm Flour) = 490 gm

so 490 gm of dough = 195 gm Carbs.

means 1 gm of dough = 195 / 490 = 0.39 gm carbs. (Carb Factor)

if you make 6 dough balls of roughly 80 gm each =>

each ball of 80 gm will have : 80 x 0.39 = 31 gm of carbs.

Means one home made roti = 31 gm.

if you eat one bread you need to give insulin for this 31 gm. (Using the ratio you learn from Doctor).

if you have missed my last article about introduction to Type 1 Diabetes you can read it here : https://medium.com/@faisalparwani/diabetes-type-1-for-dummies-1f1976c3e633

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Faisal Parwani

Software engineer for around 15+ years working in java and surrounding technologies.