Dose Calculator
This dose calculator turns a weight-based prescription into the two numbers you actually give: the single dose and the daily total. Enter the patient weight in kilograms or pounds, the prescribed rate in mg/kg, mcg/kg, or units/kg (or a fixed dose in mg), and how many times a day it is taken.
Not medical advice: this tool does arithmetic only. It does not know the drug, the patient, or the maximum safe dose, and it is not a substitute for the prescription label or a clinician’s judgment. Always confirm the result against the current FDA-approved labelling for the specific drug before any dose is given.
Not medical advice. This calculator performs the multiplication only and applies no maximum-dose limit, no renal or age adjustment, and no check against any specific drug. Confirm every result against the current FDA-approved labelling and the prescription before use.
Quick Answer
Key takeaways
- The whole calculation is two multiplications: rate times weight in kilograms gives the single dose, and the single dose times the daily frequency gives the daily total.
- Weight must be in kilograms before the multiplication. This tool converts pounds at the exact 0.453592 kg per pound, not the rough divide-by-2.2 shortcut, which is why 154 lbs gives 69.9 kg here, not 70.0 kg.
- Per-dose and per-day rates are different orders. A label written as mg/kg/day is a daily total to be divided across doses; a rate in this calculator is per dose unless you set the frequency to match a divided daily order.
- This tool applies no maximum-dose cap and no drug-specific check. The label for the actual drug, with its stated maximums, is the safety check. This page is arithmetic support, not medical advice.
- Quick Answer
- How to use this dose calculator
- The dose formula this calculator runs
- Worked examples, verified against the tool
- Per-dose rates and per-day rates are not the same order
- Why the weight has to be kilograms
- What this dose calculator does and does not check
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
How to use this dose calculator
Four inputs, in prescription order: weigh, read the rate, set the frequency, calculate.
Enter the patient's current weight. Use a measured weight, not a remembered one, and pick kg or lbs to match how it was recorded. Pounds are converted to kilograms inside the calculation, and the weight used is shown in the result so you can read it back.
Enter the prescribed dosage number. This is the figure in front of the unit on the order: the 10 in 10 mg/kg, the 5 in 5 mcg/kg, or the full amount for a fixed mg dose.
Match the dosage unit to the order. mg/kg, mcg/kg, and units/kg are per-kilogram rates. The plain mg option is a fixed dose that ignores weight in the multiplication, for orders written as a flat amount.
Set the frequency and calculate. Frequency is doses per day: 1 for once daily, 2 for twice daily, 3 for every 8 hours, 4 for every 6 hours. Read the single dose, the daily total, and the unit check line, then verify all three against the prescription and the drug label.
The dose formula this calculator runs
The formula is the standard weight-based dose equation taught in pharmacology and nursing practice, the same multiplication behind the dose calculation methods set out in the StatPearls dose calculation reference on the desired-over-have method.
Step 2, single dose: single dose = prescribed rate × weight in kg. For the fixed mg option, the single dose is the prescribed amount itself.
Step 3, daily total: daily total = single dose × frequency per day.
Worked example: 10 mg/kg × 70 kg = 700.00 mg per dose; 700.00 mg × 2 = 1400.00 mg per day.
The output unit follows the rate you picked: an mg/kg rate returns mg, an mcg/kg rate returns mcg, and a units/kg rate returns units. The calculator never converts between those output units for you. If your result is in mcg and the prescription is written in mg, stop and reconcile the units first, or run the figures through the dose conversion calculator, which exists for exactly that unit-changing job.
Worked examples, verified against the tool
Each row below was run through this calculator's code and matches its displayed output exactly, including its two-decimal formatting.
| Inputs | Single dose | Daily total | Weight used |
|---|---|---|---|
| 70 kg, 10 mg/kg, 2 times a day | 700.00 mg | 1400.00 mg | 70.0 kg |
| 154 lbs, 10 mg/kg, 2 times a day | 698.53 mg | 1397.06 mg | 69.9 kg |
| 70 kg, 500 mg fixed dose, 3 times a day | 500.00 mg | 1500.00 mg | 70.0 kg |
| 70 kg, 5 mcg/kg, 1 time a day | 350.00 mcg | 350.00 mcg | 70.0 kg |
The second row is the one worth studying. The same patient weighed in pounds does not produce the same dose as the kilogram row, because 154 lbs is 69.9 kg, not 70 kg. The 1.47 mg per-dose gap is small here, but the direction matters: every pounds entry is converted before any multiplication, so a rounded conversion never quietly inflates a dose.
Per-dose rates and per-day rates are not the same order
The most consequential reading error in weight-based dosing is mixing up a per-dose rate with a per-day rate, and it is worth being precise about which one you hold.
Many FDA-approved labels write paediatric dosing as a daily total to be divided. The DailyMed label for amoxicillin, for example, gives children over 3 months 20 to 45 mg/kg/day in divided doses every 8 to 12 hours. That figure is the whole day, split two or three ways. This calculator's rate field is per dose: enter a per-day label figure as the rate and then multiply by the frequency, and you have multiplied the day by itself, doubling or tripling the intended amount.
The safe workflow for a per-day order is to divide first: daily rate divided by doses per day gives the per-dose rate, and only then should weight enter the calculation. If your order is written per dose, as most adult weight-based orders are, enter it directly. For drug-specific orders with their own divided-dose schedules already worked out, the amoxicillin dose calculator and the semaglutide dosage calculator handle those single-drug cases, while this page stays with the general weight-based arithmetic.
Why the weight has to be kilograms
Official product labelling expresses weight-based dosing in metric units only, mg/kg and units/kg, and hospital safety guidance treats the pounds-to-kilograms step as a known error source.
The Institute for Safe Medication Practices makes metric-only weighing its Best Practice 3 in the ISMP Targeted Medication Safety Best Practices for Hospitals: obtain the patient's actual metric weight at each encounter and document weight in grams and kilograms only, because stated, estimated, or historical weights have all produced underdoses and overdoses, and a weight documented in pounds but read as kilograms has caused errors of more than twofold. This calculator follows the same discipline in miniature: it converts once, at the exact factor, and prints the kilogram weight it used next to the dose, so the conversion can be checked rather than trusted.
Children's dosing raises the stakes on the same arithmetic. Weight-based rules exist because a child's dose cannot be scaled from an adult's by age alone; the classic weight-based approach, Clark's rule, is summarised in the StatPearls reference on Clark's rule, and a review of paediatric weight estimation in the British Journal of Clinical Pharmacology literature on age-based weight estimates underlines why a measured current weight beats an estimated one. None of that changes the multiplication. It changes how carefully the weight going into it should be obtained.
What this dose calculator does and does not check
It does one job cleanly and leaves the clinical checks where they belong: with the label and the prescriber. The fuller medicine dosage calculator covers a wider set of dosage scenarios; this page is the focused weight-based tool.
What it does
- Single dose from weight and a per-kg rate in mg, mcg, or units
- Fixed mg doses that skip the weight multiplication
- Daily total from the single dose and the frequency
- Exact pounds-to-kilograms conversion, with the kilogram weight shown in the result
- A unit check line that flags mcg results, where a unit slip is a 1,000-fold error
What it does not do
- No maximum-dose cap: it will not warn if a result exceeds a drug's stated maximum
- No liquid volume or tablet count: that needs the product concentration or strength
- No body surface area, renal, age, or pregnancy adjustment
- No drug interaction, allergy, or indication check
- No substitute for the prescription: if the result and the label disagree, the label and the prescriber win
Two follow-on calculations come up often enough to name. Once a dose is set, practices sometimes need its cost, which the cost per dose calculator works out from pack price and dose size. And the pharmacy arithmetic behind concentrations, quantities, and conversions is laid out in the StatPearls pharmacy calculations reference for readers who want the methods behind the numbers.
What competing calculators miss
The top-ranking dosage tools are capable, and most of them aim wider than this page. Three gaps kept showing up.
Miss 1: the core check gets buried under extra panels. The leading weight-based dosage calculator adds liquid volume, tablet counts, course totals, and a 24-hour schedule on top of the dose. Each extra output needs an extra input, a concentration or a tablet strength, and each one is another place for a wrong figure to enter. When the question is simply "is this single dose and daily total right," the extra machinery slows the check down. This page answers that question with four inputs and shows its working.
Miss 2: the divide-by-2.2 shortcut. Widely read dosage guides teach the pounds conversion as "divide by 2.2." That gives 70.0 kg for a 154 lb patient. The exact factor gives 69.9 kg, and the doses differ: 700.00 mg against 698.53 mg per dose in the worked examples above. Small, systematic, and always in the same direction. This calculator uses 0.453592 and prints the converted weight so the difference is visible.
Miss 3: per-dose and per-day rates blurred together. Several top tools present a single rate field with no warning that many labels, amoxicillin among them, publish mg/kg/day divided across doses. Treating a per-day figure as a per-dose rate is the largest realistic error in this calculation, larger than any rounding choice, and most tools never mention it. The section above names it directly because the calculator cannot detect it for you.
One honest limit of this page, stated plainly: it has no safety cap. A specialised paediatric tool in the top results offers an optional maximum single dose field, and for children's dosing that is a genuinely useful guard. This calculator does not have one, which is why its results must be read against the drug label's stated maximums every time.
Frequently Asked Questions
Multiply the prescribed rate by the patient's weight in kilograms to get the single dose, then multiply the single dose by the number of doses per day to get the daily total. A 10 mg/kg rate for a 70 kg patient gives a 700.00 mg single dose, and twice daily gives a 1400.00 mg daily total.
Multiply the weight in pounds by 0.453592. This calculator does it automatically when you select lbs, and shows the kilogram weight in the result: 154 lbs becomes 69.9 kg. The common divide-by-2.2 shortcut gives 70.0 kg for the same patient, which slightly overstates the weight and the dose.
A per-dose rate is the amount in each single administration. A per-day rate is the whole day's amount, which the label expects to be divided across the day's doses. Entering a per-day figure into this calculator's per-dose rate field and then applying the frequency would multiply the day by itself, so divide a per-day order by the doses per day first.
It treats the amount you enter as the complete single dose, with no weight multiplication. Use it for orders written as a flat amount, such as 500 mg three times a day, which this calculator turns into a 500.00 mg single dose and a 1500.00 mg daily total.
Because 1 mg equals 1,000 mcg, so confusing the two units is a 1,000-fold dosing error, the largest unit error in everyday practice. When a result is in micrograms the calculator flags it so you read the unit back against the prescription before going further.
No. It performs the weight-based multiplication only and applies no drug-specific maximum, renal adjustment, or age adjustment. The maximum for the drug you are giving is stated in its FDA-approved labelling, and the calculated dose must be compared with that maximum before use.
No. Volume and tablet counts need the product's concentration or strength, which this calculator does not ask for. It gives the dose amount in mg, mcg, or units. Work out the volume or count from the specific product's labelled concentration, and use the dose conversion calculator if the units need changing first.
No. It is an arithmetic aid for checking a prescribed dose, not a prescribing tool and not medical advice. Dosing decisions belong to the prescriber and the current drug labelling. If a calculated result differs from the prescription or the label, stop and check with the prescriber or a pharmacist.
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References
- U.S. National Library of Medicine, DailyMed, "Amoxicillin: Dosage and Administration" - the FDA-approved label giving paediatric dosing as 20 to 45 mg/kg/day in divided doses every 8 to 12 hours. DailyMed: Amoxicillin Label, Dosage and Administration. Accessed October 2026.
- Institute for Safe Medication Practices, "Targeted Medication Safety Best Practices for Hospitals" - Best Practice 3: obtain the patient's actual metric weight and document weight in metric units only, because pounds read as kilograms have caused more than twofold dosing errors. ISMP: Targeted Medication Safety Best Practices for Hospitals. Accessed October 2026.
- StatPearls, NCBI Bookshelf, "Dose Calculation: Desired Over Have Formula Method" - the standard dose calculation methods and the conversion factors used with them, including 1 kg = 2.2 lb as an approximation. StatPearls: Dose Calculation Desired Over Have Formula Method. Accessed October 2026.
- StatPearls, NCBI Bookshelf, "Clark's Rule" - the classic weight-based paediatric dosing equation and the related weight and age rules it sits alongside. StatPearls: Clark's Rule. Accessed October 2026.
- StatPearls, NCBI Bookshelf, "Pharmacy Calculations" - pharmacy calculation methods, including weight-based dosing, body surface area, and unit conversions. StatPearls: Pharmacy Calculations. Accessed October 2026.
- British Journal of Clinical Pharmacology, via PubMed Central, "Review of commonly used age-based weight estimates for paediatric drug dosing" - why estimated weights are a weak basis for dosing and measured weights are preferred. PMC: Age-Based Weight Estimates for Paediatric Drug Dosing. Accessed October 2026.
- U.S. National Library of Medicine, DailyMed, "Amoxicillin for Oral Suspension: Dosage and Administration" - the suspension label's divided-dose schedule and its reduced upper dose for neonates and infants aged 3 months or younger. DailyMed: Amoxicillin Powder for Suspension Label. Accessed October 2026.