Medication Dosage Calculator

Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer Last updated: August 20, 2026

Disclaimer: This calculator is provided for informational and educational purposes only and does not constitute financial, medical, legal, or other professional advice. Always consult a qualified professional before making decisions based on these results.

📚 Confused about how this is calculated? Read the full The Dose Makes the Poison: The Science of Getting the Amount Right →

One Multiplication, Considerable Consequence

Weight-based dosing is the most common arithmetic in clinical medicine and the most consequential multiplication most people never think about. A prescriber reads a rate in mg/kg from the drug's labelling, multiplies by the patient's weight, and a dose falls out. The formula is trivial. Getting the inputs right — the correct rate for the correct indication, the correct weight convention, the correct units on both sides — is where the real work lies, and where errors concentrate.

The Formula

Dose (mg) = Dose per kg (mg/kg) × Weight (kg)

This calculator is deliberately generic. It is not tied to any medication, applies no maximum dose limit, and knows nothing about indication, renal or hepatic adjustment, or drug-specific rules. It multiplies the rate you supply by the weight you supply. Everything that makes a dose correct rather than merely arithmetically consistent lives outside this calculation.

Computed Dose Reference

Every cell below is the product of the row weight and the column rate:

Total dose in mg by body weight and mg/kg rate
Weight	5 mg/kg	10 mg/kg	15 mg/kg	25 mg/kg
5 kg	25	50	75	125
10 kg	50	100	150	250
20 kg	100	200	300	500
40 kg	200	400	600	1000
70 kg	350	700	1050	1750
90 kg	450	900	1350	2250

The rates shown are illustrative arithmetic, not recommendations for any drug. A real mg/kg rate comes from the medication's own labelling for the specific indication.

Where the Errors Live

Pounds entered as kilograms — a 2.2× overdose, and the single most common weight-based dosing error. Divide pounds by 2.20462 first.
Per-dose versus per-day — a rate written as mg/kg/day divided into three doses is a very different number from mg/kg per dose. The units are the instruction.
Ceiling doses ignored — many drugs stop scaling above a defined weight, so linear multiplication overshoots in larger patients. This calculator applies no such ceiling.
Actual versus adjusted weight — some agents dose on ideal or adjusted body weight rather than actual, particularly in obesity.
Concentration confusion — a dose in mg still has to become a volume in mL, which is a second calculation with its own failure modes.

Note: This is a general-purpose arithmetic reference, not medical advice. It does not know what drug you have in mind and applies no safety limits of any kind. Never use it to determine a real dose — medication dosing decisions belong with a prescriber or pharmacist working from the actual product information.

Why mg/kg at All?

Weight is a reasonable first-order proxy for the volume a drug will distribute into, so scaling by mass keeps concentration in a comparable range across body sizes. It is not the only defensible denominator: cytotoxic agents are usually dosed per square metre of body surface area, on the reasoning that surface area tracks metabolic rate better than mass does. The choice of denominator is itself a pharmacological judgement, made drug by drug.

Where This Calculation Appears

Paediatrics — nearly all children's dosing is weight-based, because the weight range across childhood is enormous.
Infusions and induction agents — anaesthetic and critical care dosing is routinely expressed per kilogram.
Anticoagulation — several agents use weight-based regimens.
Checking your own arithmetic — an independent recalculation is a standard safety practice, and this tool is fit for that narrow purpose.

How to Use This Calculator

Enter the Dose Rate (mg per kg) taken from the medication's own labelling.
Enter the Weight (kg). Confirm the unit before you type — if you have pounds, convert first by dividing by 2.20462.
Select Calculate. The result is the total dose in mg, with the multiplication shown so it can be checked at a glance.

Related Calculations

For the historical ratio-based approach to children's doses, see the Pediatric Dosage Calculator. Where the correct denominator is surface area rather than mass, use the Body Surface Area (BSA) Calculator.

Principles of Medication Dosage Calculation and Pharmacokinetics

A medication dosage calculator computes precise drug quantities based on patient body weight, body surface area, renal function, and hepatic metabolism. In clinical pharmacy and nursing practice, accurate dosage calculations prevent medication errors, the leading cause of preventable patient harm in healthcare settings.

The Five Rights of Medication Administration

Right Patient: Verify patient identity using two independent identifiers (name and date of birth).
Right Drug: Confirm medication name, formulation, and indication against the prescriber order.
Right Dose: Calculate and verify weight-based or BSA-based dosage using approved drug references.
Right Route: Confirm oral, intravenous, intramuscular, subcutaneous, or topical administration.
Right Time: Administer within the prescribed dosing schedule and frequency interval.

IV Drip Rate Calculations in Nursing Practice

IV Flow Rate (mL/hr) = Total Volume (mL) / Infusion Time (hours)
IV Drop Rate (gtt/min) = [ Total Volume (mL) × Drop Factor (gtt/mL) ] / [ Infusion Time (min) ]
Common Drop Factors: Macrodrip = 10 to 20 gtt/mL | Microdrip (Pediatric) = 60 gtt/mL

Renal and Hepatic Dose Adjustment Protocols

Medications primarily eliminated by the kidneys require Renal Dose Adjustment based on estimated CrCl or eGFR:

CrCl > 50 mL/min: Standard full dosing.
CrCl 30 to 50 mL/min: Moderate dose reduction (typically 50% to 75% of standard).
CrCl < 30 mL/min: Significant dose reduction or extended dosing intervals.

Hepatically metabolized drugs (processed by liver cytochrome P450 enzymes) require dose modifications guided by the Child-Pugh Classification Score (A, B, or C severity).

High-Alert Medications Requiring Independent Double-Check

The Institute for Safe Medication Practices (ISMP) identifies High-Alert Medications requiring mandatory independent double-verification by two licensed professionals before administration:

Insulin: All formulations (rapid-acting, long-acting, and IV insulin infusions).
Anticoagulants: Heparin drips, warfarin, and all DOACs.
Opioid Analgesics: Morphine, hydromorphone, fentanyl patches and infusions.
Chemotherapy Agents: All cytotoxic oncology medications without exception.
Concentrated Electrolytes: Potassium chloride IV infusions (> 20 mEq/100 mL).

Barcode Medication Administration (BCMA) Technology

Modern hospital systems deploy Barcode Medication Administration (BCMA) scanning at the bedside: nurses scan the patient wristband and medication barcode prior to administration, electronically verifying the Five Rights of medication safety and reducing administration errors by over 50%.

Medication Reconciliation at Care Transitions

Comprehensive medication reconciliation during hospital admission, transfer, and discharge identifies discrepancies between prescribed and administered medications, preventing potentially dangerous drug interactions and dosing errors across healthcare settings.

Precise medication dosage calculation combined with systematic safety verification protocols protects patients from preventable medication errors across all healthcare settings.