{
  "id": "urine-output",
  "version": "1fcc2a56b129",
  "status": "published",
  "name": "Urine Output Calculator",
  "question": "What is the urine output in mL/kg/h?",
  "summary": "Works out urine output in mL/kg/h from the volume collected, the body weight, and the hours, and compares it with the KDIGO 2012 urine output criteria for acute kidney injury.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/urine-output-calculator",
  "markdown": "https://www.acalculator.org/health/urine-output-calculator.md",
  "kind": "function",
  "method": "Urine output (mL/kg/h) = volume (mL) ÷ (weight (kg) × hours), rounded once to 2 decimals, halves up; the rounded rate and the hours are compared with the KDIGO 2012 urine output criteria.",
  "assumptions": [
    "The volume is all the urine collected over the hours typed, so the rate is the average over that period.",
    "The weight is the body weight typed (KDIGO 2012 does not say which weight to use).",
    "The criteria are for adults and children; newborns are not covered by this page."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "volume": {
        "title": "Urine volume (mL)",
        "description": "The urine collected over the whole period, 0 to 20,000 mL.",
        "type": "number",
        "minimum": 0,
        "maximum": 20000
      },
      "weight": {
        "title": "Weight",
        "description": "Body weight, from 1 kg to 300 kg.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 1,
        "maximum": 300
      },
      "hours": {
        "title": "Collection time (hours)",
        "description": "The hours over which the urine was collected, 1 to 72.",
        "type": "number",
        "minimum": 1,
        "maximum": 72
      }
    }
  },
  "outputs": {
    "rate": {
      "label": "Urine output (mL/kg/h)",
      "description": "Volume ÷ (weight in kg × hours), to 2 decimals.",
      "format": "number"
    },
    "perHour": {
      "label": "Urine output (mL/h)",
      "description": "Volume ÷ hours, to 1 decimal.",
      "format": "number"
    },
    "stage": {
      "label": "KDIGO 2012 urine output criterion",
      "description": "Which urine output criterion of KDIGO 2012 Table 2 the average rate over this period meets.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "volume": 300,
      "weight": "70 kg",
      "hours": 6
    },
    "outputs": {
      "rate": 0.71,
      "perHour": 50,
      "stage": "Not under 0.5 mL/kg/h: does not meet a KDIGO urine output criterion"
    },
    "text": "300 mL of urine over 6 hours at 70 kg is 0.71 mL/kg/h."
  },
  "examples": [
    {
      "given": {
        "volume": 300,
        "weight": 70,
        "hours": 6
      },
      "expect": {
        "rate": 0.71,
        "perHour": 50,
        "stage": "Not under 0.5 mL/kg/h: does not meet a KDIGO urine output criterion"
      },
      "source": "KDIGO 2012 AKI guideline, recommendation 2.1.1 (https://pmc.ncbi.nlm.nih.gov/articles/PMC4089595/); 300 ÷ (70 × 6) = 0.714, shown as 0.71: not under 0.5 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "volume": 240,
        "weight": 80,
        "hours": 8
      },
      "expect": {
        "rate": 0.38,
        "perHour": 30,
        "stage": "Stage 1 criterion: under 0.5 mL/kg/h for 6 to 12 hours"
      },
      "source": "240 ÷ (80 × 8) = 0.375, shown as 0.38: under 0.5 for 8 hours, stage 1 (KDIGO 2012, Table 2) (hand calculation)"
    },
    {
      "given": {
        "volume": 400,
        "weight": 70,
        "hours": 12
      },
      "expect": {
        "rate": 0.48,
        "perHour": 33.3,
        "stage": "Stage 2 criterion: under 0.5 mL/kg/h for 12 hours or more"
      },
      "source": "400 ÷ (70 × 12) = 0.476, shown as 0.48: under 0.5 for 12 hours, stage 2 (KDIGO 2012, Table 2) (hand calculation)"
    },
    {
      "given": {
        "volume": 300,
        "weight": 50,
        "hours": 24
      },
      "expect": {
        "rate": 0.25,
        "perHour": 12.5,
        "stage": "Stage 3 criterion: under 0.3 mL/kg/h for 24 hours or more"
      },
      "source": "300 ÷ (50 × 24) = 0.25: under 0.3 for 24 hours, stage 3 (KDIGO 2012, Table 2) (hand calculation)"
    },
    {
      "given": {
        "volume": 0,
        "weight": 70,
        "hours": 12
      },
      "expect": {
        "rate": 0,
        "perHour": 0,
        "stage": "Stage 3 criterion: anuria for 12 hours or more"
      },
      "source": "No urine for 12 hours: anuria for 12 hours or more, stage 3 (KDIGO 2012, Table 2) (hand calculation)"
    },
    {
      "given": {
        "volume": 100,
        "weight": 70,
        "hours": 4
      },
      "expect": {
        "rate": 0.36,
        "perHour": 25,
        "stage": "Under 0.5 mL/kg/h, but for less than 6 hours: no KDIGO stage yet"
      },
      "source": "100 ÷ (70 × 4) = 0.357, shown as 0.36: under 0.5, but for less than 6 hours (KDIGO 2012, 2.1.1) (hand calculation)"
    },
    {
      "given": {
        "volume": 420,
        "weight": 70,
        "hours": 12
      },
      "expect": {
        "rate": 0.5,
        "perHour": 35,
        "stage": "Not under 0.5 mL/kg/h: does not meet a KDIGO urine output criterion"
      },
      "source": "Band edge: 420 ÷ (70 × 12) = 0.50 is not under 0.5 (KDIGO 2012, Table 2) (hand calculation)"
    },
    {
      "given": {
        "volume": 300,
        "weight": 69.85322498000001,
        "hours": 6
      },
      "expect": {
        "rate": 0.72,
        "perHour": 50,
        "stage": "Not under 0.5 mL/kg/h: does not meet a KDIGO urine output criterion"
      },
      "source": "154 lb × 0.45359237 = 69.85322498 kg; 300 ÷ (69.85322498 × 6) = 0.7158, shown as 0.72 (hand calculation)"
    },
    {
      "given": {
        "volume": 249,
        "weight": 100,
        "hours": 10
      },
      "expect": {
        "rate": 0.25,
        "perHour": 24.9,
        "stage": "Stage 1 criterion: under 0.5 mL/kg/h for 6 to 12 hours"
      },
      "source": "249 ÷ (100 × 10) = 0.249, shown as 0.25: under 0.5 for 10 hours, stage 1 (KDIGO 2012, Table 2) (hand calculation)"
    }
  ],
  "sources": [
    "Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Section 2: AKI Definition. Kidney Int Suppl. 2012;2(1):19-36 (recommendation 2.1.1: urine volume under 0.5 ml/kg/h for 6 hours; Table 2, staging of AKI, urine output column; text on weight, obesity, averaging, and collection accuracy). https://doi.org/10.1038/kisup.2011.32 (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC4089595/, retrieved 2026-10-19)"
  ],
  "related": [
    "gfr",
    "creatinine-clearance",
    "fena",
    "maintenance-fluid"
  ],
  "changelog": [
    {
      "date": "2026-11-01",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    }
  ]
}