Reference

Calculators

113 free calculators that work on the page, each with its formula, normal range and how to read the result.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Hemodynamics

• Cardiac Index (CI)Cardiac output scaled to body size, so flow can be compared between a small and a large patient.
• Cardiac Output (Fick Principle)Cardiac output from oxygen consumption and the arterial-to-mixed-venous oxygen content difference (the Fick principle).
• Cardiac Output (HR × SV)Cardiac output as heart rate times stroke volume, showing which of the two is driving a change in output.
• Cerebral Perfusion Pressure (CPP)MAP minus ICP, the pressure that drives blood through the brain; the number to protect after traumatic brain injury.
• Coronary Perfusion PressureDiastolic pressure minus wedge pressure, the pressure that fills the coronary arteries, which perfuse mainly in diastole.
• Ejection Fraction (EF)Percent of end-diastolic volume ejected with each beat; the main measure of left ventricular systolic function.
• Mean Arterial Pressure (MAP)Average pressure driving blood through the organs, worked from systolic and diastolic; the usual perfusion target in shock.
• Oxygen Delivery (DO₂)Oxygen carried to the tissues each minute, cardiac output times arterial oxygen content; falls with low output, anemia or hypoxemia.
• Pulmonary Vascular Resistance (PVR)Resistance the right ventricle pumps against in the lungs; raised in pulmonary hypertension, PE and hypoxic vasoconstriction.
• Pulse PressureSystolic minus diastolic pressure; a narrow value points to low stroke volume, as in tamponade or hemorrhagic shock.
• QTc (Bazett)Heart-rate-corrected QT for judging torsades risk with QT-prolonging drugs and low potassium or magnesium; Bazett over-corrects at fast rates.
• QTc (Framingham)Heart-rate-corrected QT by a linear correction from the Framingham Heart Study, steadier than Bazett at fast and slow rates.
• QTc (Fridericia)Heart-rate-corrected QT by the cube root of RR, which corrects better than Bazett at faster rates.
• Rate Pressure ProductHeart rate times systolic pressure, an index of how hard the heart is working and how much oxygen it needs.
• Shock IndexHeart rate over systolic pressure; a rising value can flag shock before blood pressure falls.
• Stroke Volume (SV)Blood ejected per beat, worked back from cardiac output and heart rate; shows whether low output is a pump problem or a rate problem.
• Stroke Volume Index (SVI)Stroke volume scaled to body size, so pump performance can be compared between patients of different sizes.
• SVR Index (SVRI)Systemic vascular resistance scaled to body size, for judging vasodilation or vasoconstriction in patients of different sizes.
• Systemic Vascular Resistance (SVR)Afterload of the left ventricle from MAP, CVP and cardiac output; low in vasodilatory shock, high in cardiogenic and hypovolemic shock.

Respiratory

• A-a GradientAlveolar minus arterial oxygen; separates hypoxemia from hypoventilation (normal gradient) from a lung problem (wide gradient).
• Alveolar Gas Equation (PAO₂)Expected alveolar oxygen pressure from FiO2, barometric pressure and PaCO2; the first step toward the A-a gradient.
• Arterial Oxygen Content (CaO₂)Oxygen carried in each dL of arterial blood from hemoglobin, saturation and dissolved O2; shows whether anemia or hypoxemia limits delivery.
• Dead Space Fraction (Bohr)Share of each breath that is wasted ventilation, from PaCO2 and end-tidal CO2; rises with PE and overdistension.
• Driving PressurePlateau pressure minus PEEP, the pressure each breath adds; a high value means a small, stiff lung is being stretched.
• Dynamic ComplianceTidal volume over peak pressure minus PEEP; unlike static compliance it also reflects airway resistance.
• Minute VentilationRespiratory rate times tidal volume: the air moved per minute, which sets how fast CO2 is cleared.
• O₂ Extraction RatioShare of delivered oxygen that the tissues take up; rises when delivery falls or demand climbs.
• Oxygen Consumption (VO₂)Oxygen the body uses per minute, from cardiac output and the arterial-to-venous oxygen content difference.
• Oxygenation Index (OI)Mean airway pressure times FiO₂ over PaO₂: how much ventilator support it takes to oxygenate, used mostly in neonates and children.
• P/F Ratio (PaO₂/FiO₂)PaO₂ divided by FiO₂, the oxygenation measure that grades ARDS and triggers proning.
• Pleural Fluid: Exudate or Transudate (Light's Criteria)Classifies a pleural effusion as an exudate or a transudate from pleural and serum protein and LDH.
• Predicted Body Weight (PBW)Weight predicted from height and sex, the basis for lung-protective tidal volumes (6 mL/kg PBW in ARDS).
• Rapid Shallow Breathing Index (RSBI)Respiratory rate divided by tidal volume in liters during spontaneous breathing, a weaning readiness index.
• Shunt Fraction (Qs/Qt)Fraction of cardiac output that passes the lungs without picking up oxygen, as in ARDS, pneumonia and atelectasis.
• SpO₂/FiO₂ RatioSpO₂ divided by FiO₂, a stand-in for the P/F ratio when there is no blood gas; valid only with SpO₂ 97% or less.
• Static ComplianceLung and chest wall stretchiness with no flow (tidal volume over plateau minus PEEP); falls in ARDS, pulmonary edema and pneumothorax.
• Ventilator Rate for a Target PaCO₂The rate that should reach a target PaCO₂ if tidal volume, dead space and CO₂ production stay the same.

Renal & Electrolytes

• Anion GapSodium minus chloride and bicarbonate: sorts a metabolic acidosis into high-gap (lactate, ketones, toxins, renal failure) or normal-gap.
• BUN/Cr RatioBUN over creatinine; a high ratio points toward prerenal causes such as hypovolemia or GI bleeding.
• Corrected CalciumTotal calcium adjusted for low albumin; an ionized calcium is more reliable in the critically ill.
• Corrected Sodium (Hyperglycemia)Sodium adjusted for high glucose, which pulls water out of cells and lowers the measured sodium; shows the true sodium in DKA and HHS.
• Creatinine Clearance (Cockcroft-Gault)Cockcroft–Gault creatinine clearance from age, weight, creatinine and sex; the estimate most drug labels use for renal dosing.
• CRRT Effluent Dose (mL/kg/h)Total effluent rate per kg per hour, with a predilution correction, against the KDIGO target of 20–25 mL/kg/h delivered.
• Fractional Excretion of Sodium (FENa)Share of filtered sodium the kidney lets go; under 1% suggests a prerenal state, over 2% tubular injury, unless diuretics have been given.
• Fractional Excretion of Urea (FEUrea)Urea-based fractional excretion that helps separate prerenal from intrinsic kidney injury when diuretics make FENa unreliable.
• Free Water DeficitWater needed to bring a high sodium back to target, from total body water; replace it slowly.
• Sodium Change per Liter of Infusate (Adrogué-Madias)Expected change in serum sodium from 1 liter of an IV fluid, from its sodium and potassium and the total body water.
• Sodium DeficitSodium needed to reach a target level, from total body water; correct slowly to avoid osmotic demyelination.
• Urine Output (mL/kg/hr)Urine output per kg per hour, the usual way to judge kidney perfusion and stage AKI.

Acid-Base

• Albumin-corrected Anion GapAnion gap adjusted for low albumin, which otherwise hides a gap metabolic acidosis.
• Delta RatioCompares the rise in anion gap with the fall in bicarbonate to uncover a second acid-base disorder behind a gap acidosis.
• Osmolar GapMeasured minus calculated osmolality; a gap over 10 points to an unmeasured osmole such as methanol or ethylene glycol.
• Serum OsmolalityCalculated serum osmolality from sodium, glucose and BUN; compare it with the measured value to find an osmolar gap.
• Winters' FormulaExpected PaCO₂ for a metabolic acidosis (Winter’s formula); a PaCO₂ outside the range means a second, respiratory disorder.

Fluids & Resuscitation

• Intake and Output BalanceNet fluid balance for a shift or 24 hours.
• Maintenance Fluids (4-2-1 Rule)Hourly maintenance fluid by the 4-2-1 rule from weight; a starting point, not a substitute for watching intake, output and electrolytes.
• Parkland FormulaCrystalloid for the first 24 hours after a major burn, from weight and burned surface area: half in the first 8 hours from the time of injury.

Clinical Scores

• APGAR ScoreNewborn assessment at 1 and 5 minutes after birth.
• Glasgow Coma Scale (GCS)Eye, verbal and motor responses scored 3 to 15; 8 or less usually means the airway needs protecting.
• Revised Trauma ScorePhysiologic triage score from GCS, systolic blood pressure and respiratory rate.
• Richmond Agitation-Sedation Scale (RASS)Richmond Agitation-Sedation Scale from −5 (unarousable) to +4 (combative); light sedation is −2 to +1 (PADIS 2018).

Drug Calculations

• Desired Over HaveVolume to give from the ordered dose and the dose on hand; the basic dose-to-volume check.
• Drip Rate (drops/min)Gravity-drip flow in drops per minute from volume, time and the tubing drop factor.
• Half-LifeTime for a drug level to fall by half, from volume of distribution and clearance; about five half-lives to steady state or washout.
• Loading DoseFirst dose needed to reach a target drug level, from volume of distribution.
• Maintenance DoseOngoing dose rate that holds a steady-state drug level, from clearance.
• mcg/kg/min to mL/hrConverts an ordered mcg/kg/min dose into the pump rate in mL/hr for a patient weight and bag concentration.
• Push-Dose EpinephrineVolume of a 10 mcg/mL push-dose epinephrine syringe for a given dose.
• Tablets or Capsules to GiveHow many tablets make up the ordered dose.
• Weight-Based Dose (mg/kg)Turns an ordered mg/kg dose into the total dose, and into mL when you know the concentration.

Body Metrics

• Adjusted Body WeightIdeal weight plus 40% of the excess; used for dosing and creatinine clearance in obese patients.
• BMIWeight relative to height, a quick screen for underweight, overweight and obesity.
• BSA (Mosteller)Body surface area from height and weight; the divisor for the cardiac and stroke volume indices.

Pediatrics

• Pediatric Resuscitation DosesWeight-based emergency doses, energy and fluid for a child.
• Pediatric Safe Dose RangeChecks an ordered pediatric dose against the recommended mg/kg/day range.
• Pediatric Vital Sign RangesNormal heart rate, respiratory rate and systolic blood pressure by age.
• Pediatric Weight EstimateEstimates a child’s weight from age when no scale or length-based tape is available.

IV Therapy

• Infusion TimeHow long a bag will last at a set rate.
• IV Pump Rate (mL/hr)Sets the pump rate to infuse a volume over a given time.
• mcg/min to mL/hrPump rate for infusions ordered in mcg/min, such as nitroglycerin.
• Units/hr to mL/hr (Heparin, Insulin)Pump rate for infusions ordered in units per hour.

Conversions

• Length: Inches and CentimetersConverts between inches and centimeters.
• Temperature: °F and °CConverts between Fahrenheit and Celsius.
• Volume: Household and MetricConverts teaspoons, tablespoons, ounces and cups to milliliters.
• Weight: Pounds and KilogramsConverts between pounds and kilograms.

Airway & Oxygen

• Oxygen Cylinder DurationHow long a cylinder will last at a given flow.
• Pediatric ET Tube Size and DepthEstimates endotracheal tube size and insertion depth from age.

Trauma & Burns

• Burn Fluids (ABA Consensus 2 mL/kg)Initial fluid rate for major burns using the American Burn Association consensus formula.
• Burn Size (Rule of Nines)Total body surface area burned from the regions involved.
• Canadian CT Head Rule (CCHR)Decides which adults with minor head injury need a head CT, from five high-risk and two medium-risk findings.
• NEXUS Cervical Spine Criteria (NEXUS)Five findings that, when all absent after blunt trauma, identify patients who do not need cervical spine imaging.
• Ottawa Ankle and Foot RulesDecides whether an acute ankle or midfoot injury needs an ankle or foot X-ray series.
• Ottawa Knee RuleDecides whether an adult with an acute knee injury needs a knee X-ray series.

Thrombosis & Bleeding

• Bleeding Risk on Anticoagulation (HAS-BLED)Estimates 1-year major bleeding risk in atrial fibrillation patients on anticoagulation and points to the risks that can be corrected.
• Caprini VTE Risk Score for Surgery (Caprini)Estimates venous thromboembolism risk after surgery from weighted risk factors to guide prophylaxis.
• Heparin-Induced Thrombocytopenia Probability (4Ts)Pretest probability of heparin-induced thrombocytopenia from the platelet fall, its timing, thrombosis and other causes.
• Padua Prediction Score for VTE (Padua)Identifies hospitalized medical patients at high risk of venous thromboembolism who need prophylaxis.
• Pulmonary Embolism Severity Index (PESI)Predicts 30-day mortality in confirmed acute pulmonary embolism, in five risk classes.
• Simplified PESI (sPESI)Six-item version of the PESI that separates low-risk from higher-risk acute pulmonary embolism.
• Stroke Risk in Atrial Fibrillation (CHA₂DS₂-VASc)Estimates stroke and thromboembolism risk in atrial fibrillation to guide anticoagulation, with the sex-specific thresholds.
• Wells Score for PE (Wells)Pretest probability of pulmonary embolism, read in two tiers (PE likely or unlikely) and three tiers (low, moderate, high).

Critical Care Scores

• National Early Warning Score 2 (NEWS2)Scores six vital signs plus oxygen use to spot deterioration in adults and set the urgency of review.
• Pneumonia Severity Score (CURB-65)Predicts 30-day mortality in community-acquired pneumonia to guide the place of care.
• Sequential Organ Failure Assessment (SOFA)Scores dysfunction of six organ systems from 0 to 24; an acute rise of 2 or more with infection defines sepsis (Sepsis-3).

GI & Liver

• Bedside Index of Severity in Acute Pancreatitis (BISAP)Five findings in the first 24 hours that estimate the risk of in-hospital death in acute pancreatitis.
• Child-Pugh Score (CTP)Grades the severity of cirrhosis into classes A, B and C from two clinical findings and three laboratory values.
• Glasgow-Blatchford Bleeding Score (GBS)Risk score for upper GI bleeding that predicts the need for intervention and identifies very-low-risk patients (0–1) for outpatient care.
• Model for End-Stage Liver Disease (MELD 3.0)The US liver allocation score since July 2023: estimates 90-day mortality in chronic liver disease, with MELD-Na alongside.

Neuro Scores

• Intracerebral Hemorrhage Score (ICH Score)Grades spontaneous intracerebral hemorrhage at presentation and gives the 30-day mortality seen at each score.
• NIH Stroke Scale (NIHSS)The standard 15-item stroke examination: scores neurological deficit from 0 to 42.

Labs & Drug Levels

• Absolute Neutrophil Count (ANC)Neutrophils per microliter from the white count and the segmented and band percentages, with neutropenia grades.
• Phenytoin Corrected for Albumin (Sheiner-Tozer)Estimates what a total phenytoin level would be at normal albumin, with the end-stage renal disease version.

Cardiac Scores

• HEART Score for Chest Pain (HEART)Sorts emergency patients with chest pain into low, intermediate and high risk of a major cardiac event within 6 weeks.

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Not a substitute for clinical judgment or your institution’s protocols. Not affiliated with or endorsed by any certifying body (full notice in Settings).