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Dose by Weight Calculator

Converts a weight-based dose (mg/kg per dose or per day) into milligrams per administration and per day, the volume per administration for a given concentration, and applies an optional maximum single dose.

When to use

A drug reference gives a dose in mg/kg and you know the patient's weight, the dosing frequency and, optionally, the product concentration or a maximum dose.

Do not use when: The dose is based on body surface area (use body-surface-area), units are not mg/kg (e.g. mcg/kg/min infusions), or renal or hepatic adjustment is required; drug-specific references govern the actual prescription.

Formula

per_dose basis: dose_mg = dose_mg_per_kg × weight_kg; per_day basis: dose_mg = dose_mg_per_kg × weight_kg / doses_per_day; dose_mg = min(dose_mg, max_dose_mg); daily_total = dose_mg × doses_per_day; volume_ml = dose_mg / concentration_mg_per_ml

Generic arithmetic only: it does not know drug-specific limits, rounding to available strengths, or renal and hepatic adjustments. Results are informational only and not a substitute for clinical judgement or medical advice.

Inputs

ParameterTypeUnitRequiredDescription
dose_mg_per_kgnumbermg/kgyesDose in mg per kg, per administration or per day as set by dose_basis. Range: > 0, ≤ 1000
weight_kgnumberkgyesPatient weight in kilograms (the dosing weight, e.g. actual or adjusted). Range: > 0, ≤ 700
dose_basisenum: per_dose | per_daydefault per_doseWhether dose_mg_per_kg is per administration or the total for the day.
doses_per_dayintegerdefault 1Number of administrations in 24 hours (e.g. 3 for every 8 hours). Range: ≥ 1, ≤ 24
concentration_mg_per_mlnumbermg/mLnoOptional product concentration (e.g. 250 mg/5 mL = 50 mg/mL) to obtain the volume. Range: > 0, ≤ 10000
max_dose_mgnumbermgnoOptional cap per administration (often the adult dose); the calculated dose is limited to it. Range: > 0, ≤ 100000

Outputs

OutputTypeUnitDescription
dose_per_administration_mgnumbermgMilligrams per dose (after any cap).
daily_total_mgnumbermg/dayDose per administration × doses per day.
volume_per_administration_mlnumbermLDose / concentration; only when concentration_mg_per_ml is given.
daily_volume_mlnumbermL/dayOnly when concentration_mg_per_ml is given.
dosing_interval_hoursnumberh24 / doses per day.
dose_cappedbooleanTrue when the weight-based dose exceeded max_dose_mg and was limited.

Example

10 mg/kg per dose, 20 kg, 3 times daily, 50 mg/mL: {"dose_mg_per_kg":10,"weight_kg":20,"dose_basis":"per_dose","doses_per_day":3,"concentration_mg_per_ml":50} → {"dose_per_administration_mg":200,"daily_total_mg":600,"volume_per_administration_ml":4,"daily_volume_ml":12,"dosing_interval_hours":8,"dose_capped":false}

30 mg/kg/day divided in 2, 15 kg: {"dose_mg_per_kg":30,"weight_kg":15,"dose_basis":"per_day","doses_per_day":2} → {"dose_per_administration_mg":225,"daily_total_mg":450,"dosing_interval_hours":12}

15 mg/kg per dose, 60 kg, cap 500 mg: {"dose_mg_per_kg":15,"weight_kg":60,"max_dose_mg":500} → {"dose_per_administration_mg":500,"dose_capped":true}

GET https://tttkmbb.com/api/v1/calculate/dose-by-weight?dose_mg_per_kg=10&weight_kg=20&dose_basis=per_dose&doses_per_day=3&concentration_mg_per_ml=50

Machine access

Sources

FAQ

Is 'mg/kg/day' the same as 'mg/kg per dose'?

No. A daily dose is divided by the number of administrations; entering a per-day dose as per-dose would overdose by the frequency factor, which is why dose_basis is explicit.

How do I get mg/mL from a label like 250 mg/5 mL?

Divide: 250 / 5 = 50 mg/mL. For percentage solutions, 1% = 10 mg/mL.

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