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Carb-to-Insulin Ratio Calculator

Estimate a starting carb ratio from your total daily dose using the 400/450/500/550 rule, with an optional mealtime bolus.

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Insulin Sensitivity Factor CalculatorEstimate your correction factor from the total daily dose with the 1500/1700/1800/2000 rule, in mg/dL or mmol/L, plus an optional correction dose.Alcohol Calorie CalculatorAdd up the calories of a drinking session from a library of beers, wines, spirits and cocktails, with a custom-drink option.Breastfeeding Calorie CalculatorExtra daily calories while breastfeeding — about +500 kcal exclusive, with a gradual weight-loss option.Carbohydrate CalculatorEstimate your daily carbohydrate target from BMR, TDEE and your chosen carb approach.Intermittent Fasting CalculatorPlan your fasting and eating windows (16:8, 18:6, OMAD…) from your last meal time.Net Carbs CalculatorCompute net carbs from total carbs, fiber and sugar alcohols, per serving and per day.Waist-to-height ratio calculatorCompute your waist-to-height ratio and see the associated health category.Calories per meal calculatorSplit your daily calorie target evenly across your meals.

Carb-to-Insulin Ratio Calculator works straight from this page — free, instant, nothing to install. It sits under Nutrition in our catalogue, alongside Insulin Sensitivity Factor Calculator and Alcohol Calorie Calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Carb-to-Insulin Ratio Calculator?

Estimate a starting carb ratio from your total daily dose using the 400/450/500/550 rule, with an optional mealtime bolus.

When would I actually use this?

Checking a starting point for a carbohydrate ratio against the rule of thumb, or sanity-checking the ratio already set on a pump or in a régime before a meal is dosed on it.

What is the most common mistake?

Using the output as a dose. This is a starting estimate that a clinical team adjusts against real post-meal readings; the ratio also varies within a single day, typically tighter at breakfast. Nothing here knows about illness, exercise, hormones, injection site or insulin on board — the things that decide what a dose should be.

How is Carb-to-Insulin Ratio Calculator different from Insulin Sensitivity Factor Calculator?

They sit next to each other but answer different questions: Insulin Sensitivity Factor Calculator is the one to open when you need it to estimate your correction factor from the total daily dose with the 1500/1700/1800/2000 rule, in mg/dL or mmol/L, plus an optional correction dose. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Alcohol Calorie Calculator is the closest one after this: Add up the calories of a drinking session from a library of beers, wines, spirits and cocktails, with a custom-drink option.

What else is worth having open alongside it?

Breastfeeding Calorie Calculator and Carbohydrate Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The 500 rule, as taught in structured diabetes education and carried in the reference texts (Walsh & Roberts, Using Insulin; ADA Standards of Care, pharmacological therapy for type 1 diabetes): ratio in grams per unit = 500 ÷ total daily dose. The tool shows the constant it used — 450 for regular human insulin, 400 for the most insulin-resistant, 550 for the most sensitive — because the choice of constant, not the arithmetic, is what moves the answer. These are rules of thumb for a starting point, not dosing guidance.

Further reading

All guides →
ExplainerThe Carbohydrate-to-Insulin Ratio, and the Rule That Estimates ItThe ratio says how many grams of carbohydrate one unit of insulin covers, and the usual starting estimate is 500 divided by the total daily dose. Here is where that number comes from, how sharply it moves across daily doses, why a 450 version exists, and the three things it quietly assumes.ExplainerThe Insulin Sensitivity Factor and the 1800 RuleThe correction factor says how far one unit of insulin moves glucose, and the classical estimate is 1800 divided by the total daily dose in mg/dL — or 100 divided by it in mmol/L. Those are the same rule, and here is the arithmetic that proves it, plus why stacking is the error that actually hurts.ExplainerHbA1c to Average Blood Sugar: The Full Conversion TableAn HbA1c of 7 percent corresponds to an average glucose of about 154 mg/dL, or 8.5 mmol/L, or 53 mmol/mol. Here is the whole table, the formulas behind it, and when the number cannot be trusted.ExplainerBlood Sugar Units: mg/dL, mmol/L, and Why Both ExistThe conversion factor is not 18 — it is 18.016, and it is the molar mass of glucose divided by ten. Here is where it comes from, which countries use which unit, and every diagnostic threshold in both scales with the guideline it belongs to.Comparison16/8, 5:2 or Alternate Day: The Fasting Protocols ComparedFive protocols side by side, what each demands, and the uncomfortable finding from the controlled trials: matched for calories, fasting loses about the same weight as simply eating less.ExplainerWhat Breastfeeding Actually Costs in Energy — and Why the Published Number Is Smaller Than the MilkMilk production has a computable cost: volume times energy density divided by the efficiency of conversion. Do the sum and you get about 675 kcal a day, not the 500 that gets quoted. Here is the derivation, why the published increment is deliberately lower, how much the real spread is between mothers, what the water requirement actually rests on, and why cutting calories while feeding is a clinical question.