Calculators & Tools

Estimated Blood Volume Calculator

EBV by Age & Weight

1 What is the Estimated Blood Volume Calculator?

The Estimated Blood Volume Calculator computes a patient's total circulating blood volume from body weight using age-specific mL/kg values, spanning preterm neonates through adolescents/adults. Alongside the estimated blood volume (EBV), it surfaces bedside transfusion thresholds — a 10% single-draw/transfusion-start volume and a 15% haemorrhagic-shock threshold — plus the maximum allowable blood loss (MABL) formula. It is intended as a quick reference for clinicians managing phlebotomy limits, transfusion planning, or perioperative blood loss in neonates and children.

2 When to use it

  • Estimating safe single-draw or diagnostic phlebotomy volumes in neonates and small infants
  • Planning transfusion volumes or thresholds in a bleeding or anaemic child
  • Perioperative or trauma assessment of allowable blood loss before transfusion is required
  • Contextualising acute blood loss as a percentage of a patient's total blood volume
  • Quick bedside lookup when a patient's expected mL/kg band isn't immediately known

3 Formula & method

EBV = weight (kg) × mL/kg, where mL/kg is selected by age band: Preterm neonate 95 mL/kg, Term neonate (0–1 month) 85 mL/kg, Infant (1–12 months) 80 mL/kg, Child (1–12 years) 70 mL/kg, Adolescent/Adult (>12 years) 65 mL/kg. The app also derives 10% of EBV (safe single-draw/starting transfusion volume), 15% of EBV (haemorrhagic shock threshold), and Maximum Allowable Blood Loss: MABL = EBV × (Hct₀ − Hct_min) / Hct_avg.
  • Fluid and Electrolyte Formulae
  • Coté & Lerman, Practice of Anesthesia for Infants and Children, 6th ed.

4 Frequently asked questions

What mL/kg value does the app use for a term newborn?

85 mL/kg, per the Term neonate row in the app's age-band table.

How does the blood volume estimate change with age?

The app steps mL/kg down as children get older — 95 for preterm neonates, 85 for term neonates, 80 for infants, 70 for children, and 65 for adolescents/adults.

What does the 15% threshold mean?

The app flags 15% of estimated blood volume as the haemorrhagic shock threshold, at which blood should be prepared.

What is MABL?

Maximum Allowable Blood Loss, calculated in the app as EBV × (Hct₀ − Hct_min) / Hct_avg, used to estimate how much blood can be lost before transfusion is indicated.

Is the mL/kg figure exact for every patient?

The app notes that the patient ranges shown are typical and should be verified against the individual patient's clinical context.

For qualified clinicians. This page and the PediAid app are a clinical aid only. Calculations and reference data must be verified against the patient's clinical context, the source guideline and your local protocols before any treatment decision is made.