Last Updated on September 18, 2025

A carbohydrate factor (Carb Factors), also called an insulin-to-carbohydrate ratio (ICR), is one of the most important tools for managing diabetes. It tells you how many grams of carbohydrate are covered by a single unit of rapid-acting insulin.

Example: If your Carb Factor is 1:10, one unit of insulin covers 10 grams of carbs. A 50-gram meal would need 5 units.
Why it matters: An accurate Carb Factor makes meals easier to manage, helps prevent glucose spikes, and keeps blood sugars more predictable.
Starting point: Most people begin with a ratio suggested by their healthcare provider or with a formula based on weight and total daily insulin dose.
Next step: Over time, you’ll learn how to test and adjust your Carb Factor to fit your individual needs.

How to Select a Starting Carb Factors

A healthcare provider might suggest a starting point, but newer formulas based on weight and total daily insulin dose (TDD) are more accurate than older “rules of thumb.”

Insulin Pump (non-AID): CarbF ≈ (2.4 × weight in lbs) ÷ betterTDD (or 5.3 × weight in kg ÷ betterTDD).
AID systems: CarbF ≈ (2.23 × weight in lbs) ÷ betterTDD (or 4.9 × weight in kg ÷ betterTDD).

Note: “betterTDD” refers to the 14-day average TDD, which provides excellent control.

For CarbFs below 10, use decimals (e.g., 9.3 g/u) to improve accuracy.

Example: If you weigh 160 lbs and your betterTDD is 40 units, your starting CarbF would be (2.4 × 160) ÷ 40 = 9.6 g/u.

👉 Ready to dive deeper? Learn how to select, check, and adjust your Carb Factor.