{
  "id": "dosage",
  "version": "fc645c10a4b2",
  "status": "published",
  "name": "Dosage Calculator",
  "question": "How do I work out a dosage by weight?",
  "summary": "Does the arithmetic of a weight-based dosage: a prescribed dose in mg/kg times body weight, split per dose, and the liquid volume from the concentration on the label. It suggests no doses.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/dosage-calculator",
  "markdown": "https://www.acalculator.org/health/dosage-calculator.md",
  "kind": "function",
  "method": "Per dose: mg/kg × weight (kg), or mg/kg per day × weight ÷ doses per day. Volume (mL) = dose (mg) ÷ (label mg ÷ label mL).",
  "assumptions": [
    "The dose in mg/kg comes from the prescription or the drug label. The calculator does not suggest, check, or cap doses.",
    "Pounds are converted to kilograms exactly (1 lb = 0.45359237 kg).",
    "Each amount and volume is rounded to 2 decimals, halves up; each is worked out from unrounded values."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "basis": {
        "title": "The prescribed dose is",
        "description": "Whether the prescribed mg/kg is for each dose, or for the whole day split into doses.",
        "type": "string",
        "enum": [
          "dose",
          "day"
        ]
      },
      "mgkg": {
        "title": "Prescribed dose (mg/kg)",
        "description": "The dose in milligrams per kilogram of body weight, as written in the prescription.",
        "type": "number",
        "minimum": 0.0001,
        "maximum": 1000
      },
      "weight": {
        "title": "Weight",
        "description": "Body weight.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 0.3,
        "maximum": 350
      },
      "n": {
        "title": "Doses per day",
        "description": "How many doses are given in 24 hours.",
        "type": "integer",
        "minimum": 1,
        "maximum": 24
      },
      "cmg": {
        "title": "Liquid strength: mg",
        "description": "Optional: the milligrams of drug in the stated volume on the label, for example 160 in \"160 mg per 5 mL\".",
        "type": "number",
        "minimum": 0.001,
        "maximum": 100000
      },
      "cml": {
        "title": "Liquid strength: per mL",
        "description": "Optional: the volume in mL that holds those milligrams, for example 5 in \"160 mg per 5 mL\".",
        "type": "number",
        "minimum": 0.01,
        "maximum": 10000
      }
    }
  },
  "outputs": {
    "dose": {
      "label": "Each dose",
      "description": "The amount per dose in mg, to 2 decimals.",
      "format": "number"
    },
    "daily": {
      "label": "Total per day",
      "description": "The amount per day in mg, to 2 decimals.",
      "format": "number"
    },
    "volume": {
      "label": "Volume per dose (mL)",
      "description": "The liquid volume that holds one dose, in mL, to 2 decimals. Shown when the liquid strength is given.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "basis": "dose",
      "n": 4,
      "mgkg": 15,
      "weight": 20,
      "cmg": 160,
      "cml": 5
    },
    "outputs": {
      "dose": 300,
      "daily": 1200,
      "volume": 9.38
    },
    "text": "Each dose is 300 mg, 1,200 mg per day."
  },
  "examples": [
    {
      "given": {
        "basis": "dose",
        "mgkg": 15,
        "weight": 20,
        "n": 4,
        "cmg": 160,
        "cml": 5
      },
      "expect": {
        "dose": 300,
        "daily": 1200,
        "volume": 9.38
      },
      "source": "Gage and Preuss 2023, StatPearls, Dose Calculation (https://www.ncbi.nlm.nih.gov/books/NBK430836/), desired ÷ have × quantity: 15 × 20 = 300 mg; 300 ÷ 160 × 5 = 9.375 mL, shown as 9.38 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "basis": "day",
        "mgkg": 40,
        "weight": 19.958064280000002,
        "n": 2,
        "cmg": 250,
        "cml": 5
      },
      "expect": {
        "daily": 798.32,
        "dose": 399.16,
        "volume": 7.98
      },
      "source": "44 lb = 19.958 kg; 40 × 19.958 = 798.32 mg/day; ÷ 2 = 399.16 mg; 399.16 ÷ 250 × 5 = 7.98 mL (hand calculation in content.mdx)"
    },
    {
      "given": {
        "basis": "dose",
        "mgkg": 0.1,
        "weight": 70,
        "n": 1,
        "cmg": 10,
        "cml": 1
      },
      "expect": {
        "dose": 7,
        "daily": 7,
        "volume": 0.7
      },
      "source": "0.1 × 70 = 7 mg; 7 ÷ 10 × 1 = 0.7 mL (hand calculation in content.mdx)"
    },
    {
      "given": {
        "basis": "dose",
        "mgkg": 5,
        "weight": 12,
        "n": 3
      },
      "expect": {
        "dose": 60,
        "daily": 180
      },
      "source": "5 × 12 = 60 mg per dose; × 3 = 180 mg per day (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "Gage CB, Preuss CV. Dose Calculation. In: StatPearls. StatPearls Publishing; 2023. https://www.ncbi.nlm.nih.gov/books/NBK430836/ (retrieved 2026-09-29)",
    "Toney-Butler TJ, Nicolas S, Wilcox L. Dose Calculation Ratio and Proportion Method. In: StatPearls. StatPearls Publishing; 2023. https://www.ncbi.nlm.nih.gov/books/NBK499884/ (retrieved 2026-09-29)",
    "National Institute of Standards and Technology. NIST Special Publication 811, Appendix B (1 lb = 0.45359237 kg). https://www.nist.gov/pml/special-publication-811"
  ],
  "related": [],
  "changelog": [
    {
      "date": "2026-09-30",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    }
  ]
}