How to Calculate Insulin Dosing for Meals


When living with diabetes, your body is unable to produce enough insulin or use it effectively to keep your blood glucose within normal levels—especially after eating. For people with type 2 diabetes who take insulin, knowing how to calculate insulin dosing for meals can reduce spikes after eating.

In this article, we’ll explain:

  • How to calculate your insulin dosages based on your meals
  • Terms such as insulin-to-carb ratio and the insulin sensitivity factor
  • How to approximate insulin dosing using the Plate Method
  • Questions to ask your doctor about carb counting and insulin

Before we begin, please make sure you speak with your doctor before making any changes to your medication.

New to learning about mealtime insulin? Check out our guide here!

How to Calculate Insulin Dosing for Meals

Why is it important to know how to calculate insulin dosing for meals? There are many reasons why.

Calculating insulin dosing for meals:

  • Helps you stay mindful of the number of carbs in each meal, including carbohydrates from:
    • Beverages
    • Dressings, and
    • Sauces.
  • Teaches you how certain carbohydrates impact your blood glucose, and how to adjust insulin and other medication needs accordingly.
  • Reinforces food-label-reading skills, which is essential to managing diabetes.

The way to learn how much insulin you need to cover a certain number of carbs is called the insulin-to-carbohydrate ratioor, I:C.

Generally, 1 unit of insulin covers 12 to 15 grams of carbs. Jowever, this can vary depending on each person.

To learn about your insulin-to-carb ratio, work with your doctor or a nutritionist. Or, you can refer to guidelines and formulas by Gary Scheiner here.

It’s important to remember that your insulin-to-carb ratio can change depending on your insulin-sensitivity factor, which tells you how many points your blood glucose decreases per unit of insulin.

Please note that finding a ratio that works for you takes trial and error!

Example: Bolusing for a Ham and Cheese Sandwich

Let’s break it down using a ham and cheese sandwich as an example.

Our I:C is 1:15, meaning 1 unit of insulin covers 15 grams of carbs

We want to eat a sandwich that contains:

  • 2 slices of whole wheat bread
  • Ham
  • Cheese
  • Lettuce
  • Tomato
  • Mayonnaise
  • Mustard, and
  • A glass of milk.

See below for the carbohydrates of the total meal.

Whole wheat bread (2 slices) – 30g of carbs
Ham – 0g of carbs
Cheese – 0g of carbs
2 lettuce leaves – 1g of carbs
2 slices Tomato – 1g of carbs
Mayonnaise – 0g of carbs
Mustard – 0g of carbs
Semi-skimmed milk (240ml) – 12g of carbs
Total Carbs: 44 g

If our ratio is 1 unit of insulin for every 15 g of carbohydrates, here’s how we’d determine how much insulin is needed to cover the carbs for this meal.

Total Carbohydrate in Food / Carbohydrate Ratio = Units of Insulin

44 g carbohydrates / 15 g carbohydrates (ratio) = 2.9 units of insulin.

2.9 units of insulin are required for this meal.

Using the Plate Method to Approximate Carb Counting

There’s another way to approximate carb consumption using the Plate Method.

The Plate Method is a visual way of ensuring you’re eating enough non-starchy vegetables and protein while monitoring how many higher-carb foods are on your plate.

This method also assumes you’re using a 9-inch dinner plate.

General guidelines state 1 serving of carbs should be about 15 grams of carbohydrate.

With the Plate Method, you divide your plate into:

  • Half non-starchy vegetables (broccoli, cauliflower, carrots, etc.)
  • One quarter with lean protein (fish, turkey, chicken, tofu, eggs, etc.)
  • One quarter with foods higher in carbs (rice, pasta, potatoes, beans, etc.)

How Protein and Fats Affect Carb Counting and Insulin Dosing

It is also important to know that proteins and fats—despite not having a direct effect on carbohydrates—do affect the way carbohydrates are absorbed.

A food that contains carbohydrates in addition to a high protein or fat content will be absorbed more slowly, but the effect will be longer.

That is—it will not generate such a high-blood-glucose peak, but it will last longer.

You may need to adjust your ratios as you learn how various meals impact you.

Questions to Ask Your Doctor

  • How can I determine my insulin-to-carb ratio and insulin-sensitivity factor?
  • Under what circumstances should I adjust my ratio and insulin-sensitivity factor?
  • When does it make sense to use a set amount of units of insulin?
  • Is the Plate Method more suitable for me?
  • What if I miss a dose of mealtime insulin?
  • What do I do if my blood sugar is high prior to eating?
  • How do I calculate my insulin dosages while dining out?

Key Takeaways:

  • Learning how to calculate insulin dosing for meals can help you prevent blood glucose spikes after eating.
  • An insulin-to-carbohydrate ratio determines how much insulin it takes to cover how many carbs are in a meal.
  • The insulin sensitivity factor determines how many points (mg/dL) drops with 1 unit of insulin.
  • The Plate Method segments your plate into nonstarchy vegetables, starchy carbohydrates and lean protein.
  • Using the Plate Method, generally, 1 serving of carbohydrates should be about 15 grams of carbohydrate.

Type 2 Guide to Basal Insulin

Insulin for People with T2D 

Hypoglycemia Awareness and T2D 

This content was made possible by Lilly, a Founding Partner of Beyond Type 2.

Beyond Type 2 maintains editorial control over its content.

WRITTEN BY Eugenia Araiza, CDE Nutritionist, POSTED 04/13/21, UPDATED 03/19/24

Eugenia has a degree in nutrition specializing in diabetes and she is a diabetes educator. She was diagnosed with type 1 diabetes 25 years ago, she is the creator of Healthy Diabetes. She really enjoys studying and helping others in managing their different types of diabetes. She loves studying, managing type 1 diabetes and nutrition. She especially enjoys writing about the impact diabetes has in her life. She lives surrounded by the love of her family, Luis Felipe, who lives with latent autoimmune diabetes in adults (LADA) type diabetes and her teenage son, Indigo.