Pediatric Dose Calculator
The formula
What the paediatric dose tells you
The three 19th-century bedside rules — Clark, Young, Fried — computing a child’s dose from the adult dose, kept here for the comparison they enable.
Calculation: Clark (wt/70), Young (age/(age+12)), Fried (mo/150) rule comparison. Enter your inputs and every substitution is shown below the result.
Reading the result
Where the rules disagree with the drug’s mg/kg label, the label wins; the rules exist for emergencies without one.
Rules of thumb: mg/kg with max adult dose is the modern standard; BSA for oncology
Limitations and best practice
Neonates are the worst failure of all three rules — hepatic enzyme maturation is the driver and no age-in-years heuristic captures it.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Are these rules ever right?
Why does Fried use months?
Source & methodology
Clark 1864; Young; Fried; WHO.
Pediatric Dose: the number, the method and the caveats
You want to know where you stand, and a computed figure beats a remembered one every time. Searchers land on a Pediatric Dose page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
People rarely disagree about arithmetic; they disagree about assumptions that were never written down. Printing the substitution and the sensitivity ranking removes that category of disagreement for Pediatric Dose.
Health figures in Health & Medical describe populations, not individuals — Pediatric Dose places you on a distribution built from bodies like yours, and the 135.1 mg answer is a starting point for a conversation, not a diagnosis. That framing is the difference between using a health metric and being misled by one.
Nothing below is stock text pasted around a number: the worked example computes clark estimate = 135.1 mg from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — Adult dose first, at ≈10.0 % of the headline for a ten-percent error either way in that input — which is the thread the rest of this guide pulls on.
The Pediatric Dose formula, explained
Here is the complete model this tool runs — Clark (wt/70), Young (age/(age+12)), Fried (mo/150) rule comparison — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.
Age (y) (example value 4) is a quantity rather than a category — precision here is cheap and worth having. Be precise about the boundary (exact date, start of month); time inputs decide the exponent in most formulas.
Weight (kg) (example value 20) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Stay in one unit system top to bottom; conversion rounding is where small errors enter.
Adult dose (mg) (example value 473) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Figures of this kind carry safety consequences; when in doubt, use the conservative value and confirm with a professional.
Pediatric Dose on the example inputs: the complete substitution
Abstract formulas are hard to trust, so here is the complete substitution using the default inputs, written the way an examiner would want it. Starting figures: Age (y), Weight (kg), Adult dose (mg). The endpoint of that chain is 135.1 mg of clark estimate, sitting in the “The three classic rules answer 20 kg / 4 y with 135, 118 and 151 mg — a spread of 33 mg that shows why none should be trusted” band.
- Clark: 500 × 20/70 = 135.1 mg
- Young: × 4/(4+12) = 118.3 mg
- Fried: × 48 mo/150 = 151.4 mg
Young rule — 118.3. Read next to the headline, this is the figure that shows the shape of the trade-off.
Fried rule (infants) — 151.4. If your inputs change, this is usually the first companion figure to move.
mg/kg implied — 6.76. Compare it against the main result of 135.1 mg before drawing conclusions.
Use WHO mg/kg instead — rules are historical, not pharmacometric. Compare it against the main result of 135.1 mg before drawing conclusions.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
The Pediatric Dose corridor: your result across a realistic band
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| Adult dose setting | Clark estimate |
|---|---|
| 80 % of the example value | 108.1 mg |
| 90 % of the example value | 121.6 mg |
| example inputs | 135.1 mg |
| 110 % of the example value | 148.7 mg |
| 120 % of the example value | 162.2 mg |
That spread — 108.1 mg at the low end, 162.2 mg at the high — is what a careful read of Pediatric Dose looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing Adult dose alone; the substitution steps will follow your figures exactly.
Where Pediatric Dose is fragile — and where it is not
Generic advice says “it depends on your inputs”; this section says exactly how much. Each field was perturbed by ±10 % in isolation and the clark estimate recomputed, so the ranking below is measured rather than asserted. For Pediatric Dose the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Adult dose: ten percent up gives 148.7 mg, ten percent down gives 121.6 mg — ≈10.0 % of the clark estimate either way
- Nudge Weight by ±10 % and Pediatric Dose lands between 121.6 mg and 148.7 mg (sensitivity ≈10.0 %)
Adult dose is the dominant lever here: ten percent either way moves the result by about 10.0 %, from 121.6 mg to 148.7 mg. That is where a careless figure does the most damage, so check it against a source, and Weight is effectively tied with it (≈10.0 % for the same nudge), so verify the pair together. The remaining fields can sit at safe defaults without materially changing the answer — knowing which is which is what separates a careful calculation from an anxious one.
What a Pediatric Dose of 135.1 mg means in practice
The value above only becomes useful the moment you know what it is being measured against. The default case lands in the “The three classic rules answer 20 kg / 4 y with 135, 118 and 151 mg — a spread of 33 mg that shows why none should be trusted” band, and bands are deliberately wide because real situations overlap. The sensitivity list shows how far a modest input error moves you along that ladder: for Adult dose, ±10 % covers 121.6 mg to 148.7 mg. The practical reading rules: read the band as a starting hypothesis, then test it: change the two dominant inputs by ten percent and see whether the verdict survives. Verdicts that survive stress are the ones worth acting on.
Set Pediatric Dose beside its neighbours and it usually plays a specific role: this figure establishes the size of something, and the neighbouring tools establish whether that size is acceptable. Skipping the first step makes the second one arbitrary.
The errors that quietly break a Pediatric Dose figure
Neonates are the worst failure of all three rules — hepatic enzyme maturation is the driver and no age-in-years heuristic captures it. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Reading Pediatric Dose as a promise rather than a conditional. Every number here is of the form “if these inputs, then this result”; when an input moves, the honest response is to recompute rather than to defend the old figure.
This model has its own particular trap: Adult dose carries ≈10.0 % of the response per ten percent of error, so effort spent elsewhere is largely decorative.
The subtlest error is answering the wrong question precisely. Confirm that clark estimate is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.
Before you trust your Pediatric Dose: a short checklist
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Note the date and the inputs beside the number so the figure can be audited later.
- Check Adult dose before anything else: it is the measured dominant input, ≈10.0 % of Pediatric Dose per ten percent.
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Verify each input against its original source document, not memory.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
A routine for decision-grade Pediatric Dose
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — start from evidence. The inputs behind Pediatric Dose are age (y), weight (kg), adult dose (mg). Write them down with their source next to each one; if you cannot name where a figure came from, that is the input most likely to be wrong. Rounding early is the quietest way to introduce a permanent error.
Step 2 — start from the case you can defend. Enter pessimistic-but-honest figures first; the optimistic run is a ceiling, not a plan. A conclusion that holds on conservative inputs holds everywhere. Half of a good calculation is knowing which input you would hate to be wrong about.
Step 3 — isolate your variables. Change one field, observe, revert. The live sensitivity list does the ranking for the default inputs; verify it against your own, because dominance shifts when the starting point shifts. Half of a good calculation is knowing which input you would hate to be wrong about.
Step 4 — compute a corridor, not a point. Three runs — worst, likely, best — turn Pediatric Dose from a snapshot into a range. Plan against the pessimistic end and treat the optimistic end as the upside story. A result worth acting on survives having its two shakiest inputs halved.
Step 5 — record the context, not just the number. Note today’s date and the inputs alongside the 135.1 mg output. Six months from now the context is what turns this figure into a trend. If the verdict changes with a ten-percent nudge, report the nudge alongside the number.
From calculation to decision: where Pediatric Dose earns its keep
Numbers earn their keep in conversations, and Pediatric Dose is no exception. In Health & Medical discussions around Medications & Dosing, this figure decides whether an option stays on the table: it converts an opinionated debate into an arithmetic one, and arithmetic is the only referee both sides accept. The test of a good estimate is not that it feels right but that it changes what you do.
The companion outputs — Young rule and Fried rule (infants) — exist for the second stage of that screen: the headline sizes the prize, while the companions describe the trade-off you are accepting to get it. Precision is a promise you make about your data; make sure your inputs can keep it.
There is a personal-administration use people overlook: periodic self-checking. Pediatric Dose quietly drifts as life changes — rates move, bodies change, costs compound — and re-running it a few times a year catches drift while correction is still cheap. A figure nobody can reproduce is a figure nobody will act on twice.
People also ask about Pediatric Dose
What affects Pediatric Dose the most?
The short answer: Adult dose. The longer answer is the sensitivity table on this page, where every numeric input was probed by ten percent and the clark estimate recalculated — Adult dose moved it furthest, by roughly 10.0 % (121.6 mg to 148.7 mg).
Do weight and adult dose matter equally?
Pediatric Dose here is co-driven: Adult dose and Weight produced ≈10.0 % and ≈10.0 % responses, which is a tie for practical purposes. Everything below those two is a rounding error by comparison.
What is a typical Pediatric Dose?
On the worked example above Pediatric Dose comes out at 135.1 mg. Treat that as one point on a distribution rather than a norm: the bands, the companion outputs and the sensitivity ranking tell you how wide the plausible range really is.
How do I calculate Pediatric Dose by hand?
Clark (wt/70), Young (age/(age+12)), Fried (mo/150) rule comparison is the entire method. Work the inputs in that order — Clark: 500 × 20/70 = 135.1 mg — and you will reach 135.1 mg on the default figures, the same number this tool prints.
What happens to Pediatric Dose if adult dose changes by 10 %?
The engine was re-run with that field moved by ten percent while everything else stayed fixed: the clark estimate goes across 121.6 mg to 148.7 mg, a swing of roughly 10.0 % around the 135.1 mg baseline. That ratio is the practical definition of how much this input matters.
Is the Pediatric Dose result of 135.1 mg good or bad?
The tool answers “what”, not “whether”: 135.1 mg carries the verdict “The three classic rules answer 20 kg / 4 y with 135, 118 and 151 mg — a spread of 33 mg that shows why none should be trusted” for the default case, which is a starting interpretation rather than a verdict on your situation. Re-run with your own figures and compare the bands.
How accurate is Pediatric Dose for me personally?
The formula encodes averages; body-composition and measurement error typically shifts results by a few percent in either direction. Use ranges and trends, and treat any single 135.1 mg as approximate.
When should I take Pediatric Dose to a professional?
Whenever the verdict band is far from your everyday range, or the inputs include medication-influenced values. Pediatric Dose is a screening lens — a clinician holds the diagnostic instruments.
Are these rules ever right?
As sanity checks when no paediatric data exist — and they are roughly correct for linear adult-scaled drugs in older children.
Why does Fried use months?
It was built for infants (<2 y), the population where weight-in-years rules break hardest.
Can this tool see the numbers I type?
It cannot. There is no submission step: the calculation happens in your browser and the result disappears when you close the page. Treat the fields above as a scratchpad rather than a form.
Key terms on this page
- Young rule
- 118.3 for the Pediatric Dose worked case; it sits next to the main result because it carries context the headline leaves out.
- Fried rule (infants)
- 151.4 on the example inputs — a companion figure printed beside the headline of Pediatric Dose so that no result is read in isolation.
- mg/kg implied
- 6.76 on the example inputs — a companion figure printed beside the headline of Pediatric Dose so that no result is read in isolation.
- Clark estimate
- The primary output of this tool: 135.1 mg for the default inputs, computed exactly from Clark (wt/70), Young (age/(age+12)), Fried (mo/150) rule comparison.
- Worked example
- The step-by-step substitution printed above, so the arithmetic can be re-derived by hand or in a spreadsheet.
- Verdict band
- The interpretation attached to a result (“The three classic rules answer 20 kg / 4 y with 135, 118 and 151 mg — a spread of 33 mg that shows why none should be trusted” on these inputs), which turns a bare number into a position on a scale.
- Sensitivity (±10 %)
- How far the Pediatric Dose moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
The provenance of this Pediatric Dose calculation
There is no black box on this page — the engine evaluates Clark (wt/70), Young (age/(age+12)), Fried (mo/150) rule comparison. Source of record: Clark 1864; Young; Fried; WHO. Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.
This page is an estimation aid, not professional advice. The design rule is simple: two people entering identical figures must get identical answers. The sensitivity table above is part of that promise rather than a bonus: it lets you see how much of the result depends on how carefully you measured.
Turning this Pediatric Dose into a decision
If the verdict band sits far from your usual range, take the printed inputs and result to a professional — this tool screens, it does not diagnose.
The audience here is people checking a personal health figure before acting on it. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.