Sunday, July 5, 2026
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Clinical Calculator · Weight-Based Dosing

Dosage Calculator: mg/kg Weight-Based Drug Dosing

Calculate drug dosage by body weight (mg/kg), IV volume to administer, and pediatric maximum-dose checks. Built for clinicians, pharmacists, and pharma trial operations.

Quick Answer

Weight-based drug dosing calculates total milligrams from patient body weight in kilograms multiplied by the prescribed mg/kg rate—for example, 25 mg/kg in a 20 kg child equals 500 mg per dose. This free calculator converts lbs to kg, computes daily and weekly exposure, IV draw-up volume from concentration, and pediatric maximum-dose checks. Pharma teams use mg/kg dosing for protocol dose tables, PK sampling windows, oncology regimens, and label-backed pediatric references.

Calculate Drug Dosage

Select a mode, enter patient weight and prescribed dose, then calculate total dose or volume to administer.

Patient and dose
Weight (kg)
—
kg
Single Dose
—
mg / dose
Daily Dose
—
mg / day
Weekly Dose
—
mg / week
Volume to administer

Calculate the volume to draw up or administer based on dose and drug concentration.

Calculated Dose
—
mg
Dose to Give
—
mg (after cap)
Volume to Give
—
mL
Pediatric dose check

Verify pediatric dosing against adult maximum dose limits.

Calculated Dose
—
mg
Max Adult Dose
—
mg
% of Adult Max
—
%

Formulas

Mode A — Basic mg/kg Dose
Dose (mg) = Weight (kg) × Dose per kg (mg/kg)
Daily dose = Single dose × Frequency (doses/day)
Weekly dose = Daily dose × 7
If weight in lbs: kg = lbs / 2.2046
Mode B — Volume to Administer
Volume (mL) = Dose (mg) / Concentration (mg/mL)
If max dose set: Dose to give = min(Calculated dose, Max dose)
Volume reflects the capped dose
Mode C — Pediatric Dose Check
Ped. dose = Weight (kg) × Dose (mg/kg)
% of adult max = (Ped. dose / Max adult dose) × 100
Flag if calculated dose exceeds max adult dose

How to Use This Calculator

1
Select your calculation mode: mg/kg Dose for total dose from weight, Volume to Give to find how many mL to draw up, or Pediatric Check to verify dose against adult maximum.
2
Enter the patient's weight in kg or lbs — the calculator converts lbs to kg automatically (÷ 2.2046).
3
Enter the prescribed dose in mg/kg as ordered by the prescriber or listed in the protocol dose table.
4
Click Calculate to get the total dose in mg, daily dose, weekly dose, and volume if applicable.
Worked Example

Amoxicillin for a child: 25 mg/kg/dose, 20 kg patient, 3 times daily
Single dose = 25 × 20 = 500 mg per dose
Daily dose = 500 × 3 = 1,500 mg/day

Volume to give: Amoxicillin 250 mg/5 mL suspension = 50 mg/mL
Volume = 500 mg / 50 mg/mL = 10 mL per dose

Pharma & clinical trial context

Weight-based mg/kg dosing appears throughout investigational and marketed product protocols: antibiotic and antiviral regimens in infectious disease trials, pediatric PK substudies with sparse sampling windows, and dose-escalation cohorts where mg/kg tiers map to fixed protocol dose levels. Sponsors document exact mg/kg values, maximum caps, and dose-modification rules in the pharmacy manual and statistical analysis plan.

PK sampling schedules often anchor blood draws to post-dose time points relative to the calculated mg/kg dose (e.g., Cmax at 1–2 hours after oral administration). Loading and maintenance strategies for drugs with long half-lives are modeled separately—use our Loading Dose Calculator and Maintenance Dose Calculator when target concentration and clearance drive the regimen rather than a fixed mg/kg rate alone.

Renal and BSA-based adjustments sit alongside weight-based math. Many labels cap mg/kg results when creatinine clearance or eGFR falls below thresholds—cross-check with our GFR Calculator and Creatinine Clearance Calculator. Oncology and some biologic protocols use mg/m² instead of mg/kg; calculate BSA with our BMI / BSA Calculator before applying protocol dose tables.

Evidence & sources

Frequently Asked Questions

mg/kg dosing is weight-based dosing where the drug amount is calculated per kilogram of body weight. For example, a dose of 25 mg/kg for a 20 kg patient equals 500 mg per administration. This approach scales drug exposure to body size and is standard for many antibiotics, anticonvulsants, and pediatric regimens in FDA labeling and clinical trial protocols.
Divide weight in pounds by 2.2046. For example, 154 lbs ÷ 2.2046 ≈ 69.9 kg. Accurate kg conversion matters because mg/kg calculations use kilograms exclusively. This calculator performs the conversion automatically when you select lbs in the weight field.
Children have different body composition, metabolic rates, and organ maturity compared to adults. Weight-based dosing ensures drug exposure is appropriate relative to body size, reducing the risk of under-dosing (treatment failure) or over-dosing (toxicity). Many pediatric labels specify mg/kg with maximum single-dose or daily caps that this calculator can help verify.
A loading dose is a higher initial dose administered to rapidly achieve therapeutic drug concentrations. It is followed by lower maintenance doses to sustain those levels. Loading doses are used for drugs with long half-lives or when a rapid therapeutic effect is needed (e.g., phenytoin, vancomycin, digoxin). Use our Loading Dose Calculator when you need to estimate loading dose from target concentration and volume of distribution.
Volume (mL) = Dose (mg) ÷ Concentration (mg/mL). For example, if you need to administer 500 mg and the drug is available at 50 mg/mL: Volume = 500 ÷ 50 = 10 mL. Use Mode B (Volume to Give) in this calculator to compute draw-up volume after weight-based dose calculation and optional maximum-dose capping.
Per dose refers to a single administration amount. Per day is the total drug given across all doses in 24 hours. For example, amoxicillin 500 mg per dose given 3 times daily equals 1,500 mg per day. This distinction matters for assessing total drug exposure, adherence, and comparing against label maximum daily doses in trials and bedside practice.
Use mg/m² body surface area (BSA) dosing for many oncology chemotherapies, some biologics, and protocol-specified regimens where exposure is normalized to BSA rather than weight alone. mg/kg remains common for antibiotics and many pediatric drugs. When a protocol or label specifies mg/m², calculate BSA first with our BMI/BSA Calculator, then apply the mg/m² rate—not mg/kg.
Weight-based mg/kg calculations determine the initial dose magnitude; renal impairment may require dose reduction, interval prolongation, or contraindication regardless of weight. Drug labels and trial protocols reference creatinine clearance (CrCl) or eGFR thresholds for renally cleared agents. After calculating mg/kg dose, cross-check renal function with our GFR Calculator or Creatinine Clearance Calculator and apply label-specific adjustment tables.
Oncology protocols often express cytotoxic and supportive drug doses as mg/m² per cycle or per day (e.g., carboplatin AUC-based dosing uses GFR; many agents use flat mg/m² tables). BSA is typically calculated via DuBois or Mosteller from height and weight. mg/kg alone does not replace protocol dose tables for chemotherapy—always apply the trial-specific dose level, renal/hepatic modification rules, and cumulative caps.
Maximum dose caps limit the calculated mg/kg dose to a fixed ceiling (e.g., adult maximum single dose) to prevent toxicity when weight-based math would exceed safe exposure. Pediatric labels often cap mg/kg results at adult-equivalent maxima. Mode B and Pediatric Check modes in this calculator apply optional max-dose limits. Caps appear in FDA labeling, institutional policies, and trial dose-modification tables.
Round to a practical measurable amount per local pharmacy policy and drug formulation—often to the nearest 0.1 mL for liquids or whole/half tablets for solids. Clinical trials may specify rounding rules in the pharmacy manual (e.g., round to nearest 5 mg). Do not assume one rounding convention across all drugs; verify the protocol pharmacy instructions or current prescribing information before administration.
Bedside mg/kg calculation converts weight and prescribed rate to milligrams for a single order. Trial protocol dosing adds fixed dose levels, cohort-specific tables, PK sampling windows, dose-modification rules for toxicity or organ impairment, and blinding requirements. Sponsors document exact mg/kg or mg/m² values in the pharmacy manual; calculators support verification but do not replace protocol-mandated dose levels, randomization assignments, or medical monitor review.

Related Calculators

LD Loading Dose Calculator MD Maintenance Dose Calculator GFR GFR Calculator CrCl Creatinine Clearance BSA BMI / BSA Calculator

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