5 min read 4 steps 5 terms 3 examples 6 FAQs single dose (mg) = weight (kg) × dose rate (mg/kg)

Children are not small adults — a dose that is safe for a 40 kg child can be an overdose for a 12 kg toddler.

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Walk-through

How to Use This Calculator

4 steps

Enter the child's weight

Enter the patient's weight in kilograms — use the most recent measured weight, not an estimate. If you only have pounds, switch the unit toggle to lb and the calculator converts to kilograms automatically (×0.4536).

Enter the dose and frequency

Enter the dose rate in mg/kg per dose and how many doses are given per day. These come from the prescriber's order or the drug reference — the calculator does not know the right rate for a given drug.

Add the concentration

For liquid medicines, enter the concentration as an amount in mg per a volume in mL (for example 250 mg / 5 mL). The calculator converts the dose in mg into the volume to draw up in mL.

Check the safe range

On the Safe Range Check tab, enter the typical minimum and maximum mg/kg/day for the drug. The calculator compares this dose's mg/kg/day against that range and against an optional single-dose cap, and shows a within / under / over verdict.

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Reference

Formula & Methodology

3 formulas

Single dose (weight-based)

single dose (mg) = weight (kg) × dose rate (mg/kg)

Pediatric doses are scaled to body weight so a child of any size receives a proportional amount. Example: a 20 kg child at 10 mg/kg receives 20 × 10 = 200 mg per dose.

Daily total and mg/kg/day

daily total (mg) = single dose × doses/day · mg/kg/day = dose rate × doses/day

The daily total is the single dose multiplied by the number of doses per day. The mg/kg/day figure is what you compare against the drug's safe range. Example: 200 mg × 3 = 600 mg/day, and 10 mg/kg × 3 = 30 mg/kg/day.

Volume to administer

volume (mL) = single dose (mg) ÷ concentration (mg/mL), where concentration = amount ÷ volume

Liquid medicines are labeled as an amount per a volume. Convert that to mg per mL, then divide the dose by it. Example: 250 mg / 5 mL = 50 mg/mL, so 200 mg ÷ 50 mg/mL = 4.00 mL per dose.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Medical-Source Review · Updated 2026-06-14 · 2 sources

Editorial accountability

Author: {{^authorProfileUrl}}Calculover Editorial Team{{/authorProfileUrl}} - Author

Owner: Calculover Editorial Team - Editorial owner

Reviewer: Calculover Medical-Source Review - Clinical reference review

Last reviewed: 2026-06-14

Last verified: 2026-06-14

Data effective: 2026-06-14

Methodology

The Pediatric Dosage Calculator performs standard weight-based dosing arithmetic on user-entered values: single dose (mg) = weight (kg) × dose rate (mg/kg); daily total = single dose × doses per day; mg/kg/day = rate × doses per day; volume (mL) = dose (mg) ÷ concentration (mg/mL). Pounds convert to kilograms at ×0.453592. It checks mg/kg/day against a user-supplied safe range and an optional single-dose cap. No drug database is bundled — the user supplies the mg/kg rate and concentration from the order or drug reference.

Assumption: The patient weight, mg/kg dose rate, frequency, and concentration are taken from a current prescriber order or an authoritative drug reference.

Assumption: The weight is entered in the unit selected (kg or lb) and has not been mixed up — dosing pounds as kilograms would more than double the dose.

Assumption: The safe minimum and maximum (mg/kg/day) and any single-dose cap are appropriate for the specific drug, formulation, age, and indication.

Limitations & guidance

This tool does the arithmetic only; it has no drug database and cannot determine whether a medication, route, rate, or frequency is appropriate for a particular child.

Pediatric dosing can also depend on age, gestational status, kidney and liver function, allergies, interactions, indication, and maximum daily limits not captured here.

Decimal-point, unit, and concentration errors can cause serious harm — never use this calculator to create, change, or verify a medication dose without a licensed prescriber or pharmacist.

Professional guidance: The Pediatric Dosage Calculator is for health education and calculation transparency only. It is not medical advice, diagnosis, treatment, or a substitute for care from a licensed healthcare professional. Pediatric dosing must be verified by a licensed prescriber or pharmacist against the current drug reference and the order. Do NOT use this tool to self-dose a child.

Primary sources

Learn About Your Medicines - U.S. Food and Drug Administration

Giving Liquid Medicine Safely to Children - U.S. Food and Drug Administration

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Glossary

Key Terms Explained

5 terms

mg/kg dosing A dosing method that scales the dose to body weight in milligrams of drug per kilogram. It keeps the dose proportional across children of different sizes and is the standard approach for pediatric medication.

Concentration How much drug is in a given volume of liquid, written as an amount per volume (e.g. 250 mg / 5 mL). Dividing the amount by the volume gives mg per mL, which is used to convert a dose in mg into a volume in mL.

mg/kg/day The total daily dose per kilogram of body weight — the dose rate multiplied by the number of doses per day. This is the figure compared against a drug's published safe daily range.

Daily maximum The largest amount of a drug considered safe over 24 hours, often expressed as mg/kg/day or as an absolute single-dose or daily cap. Doses above the maximum should be verified with a prescriber or pharmacist.

Weight-based dosing Calculating a dose from the patient's measured weight rather than using a fixed adult dose. Essential in pediatrics, where weights span a wide range and a fixed dose could under- or over-treat.

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Scenarios

Real-World Examples

3 worked examples

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Amelia

20 kg child, 10 mg/kg, 250 mg / 5 mL, 3×/day

Weight 20 kg Dose 10 mg/kg per dose Frequency 3 doses/day Concentration 250 mg / 5 mL

Single dose = 20 × 10 = 200 mg. Concentration = 250 ÷ 5 = 50 mg/mL, so volume = 200 ÷ 50 = 4.00 mL per dose. Daily total = 200 × 3 = 600 mg, and 10 × 3 = 30 mg/kg/day. With a safe range of 20–40 mg/kg/day, 30 is within range.

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Noah (entered in pounds)

33 lb toddler, 15 mg/kg acetaminophen, 160 mg / 5 mL

Weight 33 lb (= 14.97 kg) Dose 15 mg/kg per dose Concentration 160 mg / 5 mL

33 lb converts to about 14.97 kg. Single dose = 14.97 × 15 ≈ 225 mg. Concentration = 160 ÷ 5 = 32 mg/mL, so volume ≈ 225 ÷ 32 ≈ 7.0 mL. This shows why the unit matters: dosing 33 as kilograms instead of converting would more than double the dose.

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Over the maximum

20 kg child, 20 mg/kg, 4×/day

Weight 20 kg Dose 20 mg/kg per dose Frequency 4 doses/day Safe range 20–40 mg/kg/day

mg/kg/day = 20 × 4 = 80 mg/kg/day, which is double the 40 mg/kg/day maximum. The verdict turns red: 'exceeds typical max — verify the order'. Re-check the weight unit, the mg/kg figure, and the frequency before giving this dose.

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Deep Dive

How Weight-Based (mg/kg) Pediatric Dosing Works

5 chapters · 5 min read

Children are not small adults — a dose that is safe for a 40 kg child can be an overdose for a 12 kg toddler. Pediatric medicines are therefore dosed by body weight, in milligrams per kilogram (mg/kg). This calculator turns a weight and an mg/kg rate into a dose in milligrams, converts that to the volume of liquid to measure, totals the day, and checks the result against a safe range. It does the arithmetic so you can focus on confirming the inputs.

Why pediatric dosing is weight-based

Drug effects depend on how much medicine reaches the bloodstream relative to body size. Across the wide weight range of childhood, a single fixed dose would under-treat larger children and risk toxicity in smaller ones. Weight-based dosing solves this by expressing the dose as milligrams per kilogram: multiply the rate by the child's weight in kilograms to get the dose. Because the result is only as accurate as the weight, always use a recent measured weight in kilograms rather than an estimate or an age-based guess.

Reading a concentration and converting mg to mL

Liquid medicines are labeled as an amount of drug in a stated volume — for example 250 mg / 5 mL or 160 mg / 5 mL. Divide the amount by the volume to get the concentration in milligrams per milliliter (250 ÷ 5 = 50 mg/mL). To find how much liquid to give, divide the dose in milligrams by that concentration: a 200 mg dose at 50 mg/mL is 4 mL. Concentrations differ between products and have been reformulated over the years, so always read the number printed on the specific bottle in your hand rather than relying on memory from a previous purchase.

The safe-range concept

Most drugs have a published range of total daily dosing, written as mg/kg/day. This calculator computes the dose's mg/kg/day (the rate times the number of doses per day) and compares it against the minimum and maximum you enter. A result within the range is consistent with typical dosing; below the range may be sub-therapeutic; above the range should never be given without verifying the order. You can also set a single-dose cap — an absolute ceiling in milligrams that protects larger children from exceeding the adult maximum even when the mg/kg math allows it.

Measuring liquid medicines accurately

Volumes rarely land on a round number. Use an oral dosing syringe or the device that comes with the medicine — household teaspoons vary in volume by as much as 30%, which matters for drugs with a narrow safety margin. Round the measured volume to an increment your syringe can actually deliver (commonly 0.1 mL), and when a dose sits near a maximum, round down and confirm with the pharmacist rather than rounding up. If anything about the weight, the unit, or the concentration is unclear, a pharmacist can verify the calculation in under a minute.

This calculator is for educational reference only

This tool performs the dosing arithmetic only. It does not contain a drug database and does not know whether a particular medicine, route, mg/kg rate, or frequency is appropriate for a specific child — that judgment belongs to a licensed prescriber and pharmacist, who account for age, organ function, allergies, interactions, indication, and the exact product. Use the result to check your own math and to catch unit mix-ups, not to decide or change a dose. Pediatric doses must always be verified against the current order and drug reference by a qualified clinician before they are given.

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Questions

Frequently Asked Questions

6 questions

How do I calculate a mg/kg dose?+

Multiply the child's weight in kilograms by the dose rate in mg/kg. For example, a 20 kg child at 10 mg/kg receives 20 × 10 = 200 mg per dose. To get the daily total, multiply the single dose by the number of doses per day (200 × 3 = 600 mg/day).

How do I convert pounds to kilograms for dosing?+

Divide pounds by 2.2046, or multiply by 0.4536. For example, 44 lb ÷ 2.2046 ≈ 20 kg. Switch the unit toggle in the calculator to lb and it converts automatically. Dosing a weight in pounds as if it were kilograms is a classic, dangerous error that more than doubles the dose — always confirm the unit.

How many mL is my dose?+

Divide the dose in milligrams by the concentration in mg per mL. The concentration is the labeled amount divided by its volume — for example 250 mg / 5 mL = 50 mg/mL. So a 200 mg dose is 200 ÷ 50 = 4.00 mL. Measure with an oral syringe, not a kitchen spoon.

What if the dose exceeds the maximum?+

Do not give it. A result above the safe maximum (or above a single-dose cap) turns the verdict red. First re-check the inputs — especially whether the weight is in kilograms rather than pounds, the mg/kg rate, and the frequency. Then confirm the order with the prescriber or pharmacist before administering.

Is this a substitute for a pharmacist or prescriber?+

No. This calculator does the arithmetic only — it has no drug database and cannot judge whether a medicine, route, rate, or frequency is right for a particular child. Always have pediatric doses verified by a licensed prescriber or pharmacist against the current order and drug reference. Do not use it to self-dose a child.

Why does the volume come out as a fraction like 4.37 mL?+

Doses rarely divide evenly into a round volume. The calculator shows two decimal places. Round to an increment your oral syringe can measure (usually 0.1 mL) and, for doses near a maximum, round down rather than up. If unsure, ask the pharmacist which device and rounding to use.

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Medication (example)	Concentration	= mg/mL
Amoxicillin suspension	250 mg / 5 mL	50 mg/mL
Amoxicillin suspension	400 mg / 5 mL	80 mg/mL
Children’s acetaminophen	160 mg / 5 mL	32 mg/mL
Children’s ibuprofen	100 mg / 5 mL	20 mg/mL
Infant ibuprofen (older formulations)	50 mg / 1.25 mL	40 mg/mL

Pediatric Dosage Calculator

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