How To Calculate Insuline Unite Easily
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How to Calculate Insulin Units
Insulin dosing relies on three core calculations. Here is each one explained simply.
1. Total Daily Dose (TDD)
This is the starting point for everything else.
Formula:
TDD = 0.5 to 1 unit × body weight (kg)A common starting point is 0.5 units/kg/day for new starts (conservative) or 0.75 units/kg/day for most patients.
Example: A 70 kg adult
- TDD = 0.5 × 70 = 35 units/day
Once you have the TDD, split it:
- ~50% as basal (long-acting) insulin (e.g., glargine, detemir)
- ~50% as bolus (rapid-acting) insulin spread across meals (e.g., lispro, aspart)
Harriet Lane Handbook, 23rd ed. - Johns Hopkins Hospital
2. Carbohydrate Coverage Ratio (ICR) - "How much insulin covers my food?"
This tells you how many grams of carbohydrate 1 unit of rapid-acting insulin covers.
Formula (Rapid-acting like lispro/aspart):
ICR = 500 ÷ TDD
Formula (Regular insulin):
ICR = 450 ÷ TDD
Example: TDD = 35 units
- ICR = 500 ÷ 35 = ~14 → 1 unit covers every 14 g of carbs
At mealtime:
Meal dose = Total carbs eaten ÷ ICR
Example: You eat 56 g of carbs, ICR = 14
- Meal dose = 56 ÷ 14 = 4 units
3. Correction Factor (CF) - "How much insulin lowers my high blood sugar?"
Also called the Insulin Sensitivity Factor (ISF). This tells you how much 1 unit will lower your blood glucose (BG).
Formula (Rapid-acting):
CF = 1800 ÷ TDD
Formula (Regular insulin):
CF = 1500 ÷ TDD
Example: TDD = 35 units
- CF = 1800 ÷ 35 = ~51 → 1 unit drops BG by ~51 mg/dL
Correction dose at mealtime:
Correction units = (Current BG - Target BG) ÷ CF
Example: Current BG = 220, target = 100, CF = 51
- Correction = (220 - 100) ÷ 51 = 120 ÷ 51 = ~2.5 units
4. Total Mealtime Dose
Combine both:
Total bolus = Meal dose + Correction dose
Full example:
- Current BG = 220 mg/dL, eating 56 g of carbs
- TDD = 35 units, ICR = 14, CF = 51, Target BG = 100
- Meal dose = 56 ÷ 14 = 4 units
- Correction = (220 - 100) ÷ 51 = 2.5 units
- Total bolus = 6.5 units
Quick Summary Table
| What you're calculating | Formula | Example (TDD = 35) |
|---|---|---|
| Total Daily Dose | 0.5 - 1 unit × kg | 0.75 × 70 kg = 52.5 u |
| Basal dose | TDD ÷ 2 | 52.5 ÷ 2 = 26 u/day |
| Carb ratio (rapid) | 500 ÷ TDD | 500 ÷ 35 = 1:14 g |
| Correction factor (rapid) | 1800 ÷ TDD | 1800 ÷ 35 = 51 mg/dL per unit |
| Meal dose | Carbs eaten ÷ ICR | 56 ÷ 14 = 4 units |
| Correction dose | (BG - target) ÷ CF | (220 - 100) ÷ 51 = ~2.5 units |
Important Notes
- Never adjust insulin on your own - always work with your doctor or diabetes care team to confirm starting doses and titrate.
- These formulas are starting estimates - individual responses vary and doses must be fine-tuned over days/weeks.
- Hypoglycemia risk is real - if in doubt, dose conservatively and recheck BG 2 hours later.
- For mmol/L users (common outside the US), the correction factor formula uses 100 ÷ TDD instead of 1800 ÷ TDD.
Sources: Harriet Lane Handbook 23rd ed. (Johns Hopkins), Textbook of Family Medicine 9th ed.
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