Insulin-to-Carb Ratio Calculator
Estimate how many grams of carbohydrate one unit of insulin covers, from your total daily dose, using the 500 or 450 rule. For education only: your real ratios come from your diabetes care team. Nothing you enter is stored.
Your data is not stored or sent to the server. All calculations are performed locally in your browser.
- It uses general rules of thumb. Your own ratios and correction factor should come from your diabetes care team and can differ a lot from these estimates.
- It is for education and for discussing settings with your team. Do not use it to change your insulin doses on your own.
- A wrong insulin dose can cause dangerous low or high blood sugar. If you feel unwell, follow your care plan or get medical help.
Carb ratio by total daily dose
Rule-of-thumb estimates, as units : grams of carbohydrate.
| Total daily dose | 500 rule (rapid-acting) | 450 rule (regular) |
|---|---|---|
| 20 units | 1 : 25 | 1 : 23 |
| 30 units | 1 : 17 | 1 : 15 |
| 40 units | 1 : 13 | 1 : 11 |
| 50 units | 1 : 10 | 1 : 9 |
| 60 units | 1 : 8 | 1 : 8 |
| 80 units | 1 : 6 | 1 : 6 |
How it's calculated
Rapid-acting: grams of carbohydrate per unit = 500 ÷ total daily doseRegular insulin: grams of carbohydrate per unit = 450 ÷ total daily doseSources: Texas DSHS Diabetes Toolkit: Insulin Pump Therapy
Last reviewed
Frequently asked questions
What is an insulin-to-carb ratio?
It is how many grams of carbohydrate one unit of mealtime insulin covers. A ratio of 1:10 means one unit for every 10 g of carbs, so a 60 g meal would need 6 units before any correction.
What is the 500 rule?
Divide 500 by your total daily insulin dose to estimate how many grams of carbohydrate one unit of rapid-acting insulin covers. With 50 units a day, 500 ÷ 50 = 10 g per unit.
What is the 450 rule?
Some diabetes educators find that dividing 450 rather than 500 by the total daily dose works better for regular (short-acting) insulin or for people who are more insulin resistant.
Why might my ratio differ at different meals?
Many people are more insulin resistant in the morning, so breakfast often needs a stronger ratio (fewer grams per unit) than lunch or dinner. Care teams commonly set separate ratios for each meal.
How accurate is the estimate?
It is a starting point. Care teams refine ratios by comparing readings before and a few hours after meals with known carbohydrate. Don't change your ratio without talking to them.
Related calculators
All diabetes tools- Insulin Sensitivity Factor CalculatorEstimate how far one unit of insulin lowers your blood sugar with the 1800 or 1500 rule, in mg/dL and mmol/L.
- Bolus Insulin CalculatorSee how a mealtime insulin dose is worked out from carbs, your ratio, your reading and your correction factor.
- A1c CalculatorConvert an HbA1c result to estimated average glucose, or estimate A1c from your average blood sugar.