Insulin-to-Carb Ratio Calculator
Calculate how many grams of carbohydrate one unit of insulin covers - a key number for accurate mealtime dosing.
Educational estimator only - not medical advice.
Typical range: 10-150 units/day
Enter your Total Daily Dose above to calculate your Insulin-to-Carb Ratio.
The Insulin-to-Carb Ratio (ICR) tells you how many grams of carbohydrate one unit of rapid-acting insulin will cover. It is calculated using the 500 Rule:
The number 500 was derived empirically - it reflects that the average person with diabetes who takes 1 unit of rapid-acting insulin can cover approximately 500 / TDD grams of carbohydrate while keeping blood glucose stable.
When estimating TDD from body weight, a common starting point is 0.5 units per kg for adults with Type 1 diabetes who are not significantly insulin-resistant. This estimate can vary considerably based on activity, stress, illness, and individual physiology.
Your ICR may differ at different times of day - many people need a lower (stronger) ratio at breakfast due to the dawn phenomenon.
Dive deeper into insulin-to-carb ratios, how to test and refine your personal ratio, and how to use it effectively for every meal - covered in detail in the FOD Trilogy.
Deep Dive: FOD Trilogy - Ch 11This calculator provides an estimated starting point only. Insulin dosing is a safety-critical medical decision. Incorrect insulin doses can cause hypoglycemia (dangerously low blood sugar), which can be life-threatening. Always work with your healthcare provider, endocrinologist, or certified diabetes educator to determine, test, and adjust your personal Insulin-to-Carb Ratio. Never change your insulin regimen based solely on this tool. Individual results vary significantly based on insulin type, activity, diet, illness, stress, and other factors.