T1D glossary

Insulin-to-carbohydrate ratio (ICR)

Also called carb ratio, I:C.

The insulin-to-carbohydrate ratio is the number of grams of carbohydrate that one unit of insulin covers. A bolus calculator uses it for the meal part of a bolus. A care team sets the ratio, and ADA guidance says to change it when glucose after meals is often out of target even though the carb count is accurate. (OpenAPS documentation; ADA Standards of Care 2026, section 9; ADA Standards of Care 2026, section 7)

Formula

Meal insulin (units) = grams of carbohydrate ÷ ICR (g/U)

Worked example

Arithmetic only: with an ICR of 15 g/U, a meal of 45 g works out to 45 ÷ 15 = 3 units. With an ICR of 10 g/U, the same meal works out to 4.5 units.

Related terms

• Insulin sensitivity factor
• Bolus
• Insulin on board
• Pre-bolus

Sources, quoted

• OpenAPS documentation: “CR - Carb Ratio, or carbohydrate ratio - the amount of carbohydrates that are covered by one unit of insulin.”
• ADA Standards of Care 2026, section 9: “Mealtime insulin: if carbohydrate counting is accurate, change ICR if glucose after meal consistently out of target.”
• ADA Standards of Care 2026, section 7: “Health care professional input and education can be helpful for setting the initial dosing calculations with ongoing follow-up for adjustments as needed.”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.