Pediatric Blood Volume Calculator

Estimate total blood volume from body weight and age group, then calculate the allowable blood loss before transfusion is typically considered.

Quick Facts

Blood volume by age
70-100 mL per kg
Premature infants run highest (about 100 mL/kg); the ratio falls toward about 70 mL/kg by adolescence.
Allowable blood loss
EBV x (Hi - Hf) / Hi
Estimates the volume that can be lost before hematocrit falls to a chosen target level.

Your Results

Calculated
Estimated blood volume
-
Weight x mL/kg for age group
Blood volume (liters)
-
Same estimate, in liters
Allowable blood loss
-
Before transfusion is typically considered
Allowable loss per kg
-
Normalized to body weight

Ready

Enter the child's weight, age group, and hematocrit values, then calculate.

About the Pediatric Blood Volume Calculator

Estimated blood volume (EBV) in children is calculated as body weight in kilograms multiplied by an average blood volume factor that varies by age. Younger children carry more blood per kilogram of body weight than adults do, so pediatric references group patients by age band rather than using one constant for every size.

The standard blood-volume-per-kilogram table

  • Premature infants: approximately 100 mL/kg
  • Full-term neonates (0-1 month): approximately 90 mL/kg
  • Infants (1 month-1 year): approximately 80 mL/kg
  • Children (over 1 year to puberty): approximately 75 mL/kg
  • Adolescents and adults: approximately 70 mL/kg

Multiplying the selected factor by body weight gives the estimated blood volume (EBV) in milliliters.

Allowable blood loss

A common companion calculation estimates how much blood can be lost before hematocrit falls to a chosen target level: Allowable Blood Loss = EBV x (Starting Hematocrit - Target Hematocrit) / Starting Hematocrit. This simplified formula assumes lost blood is replaced with a fluid that does not itself carry red cells (isovolemic hemodilution) and does not model ongoing losses, transfusion timing, or clinical status during a procedure.

Important disclaimer

This tool performs standard arithmetic for education and planning. It is not a transfusion order and does not replace clinical judgment. Blood volume and transfusion decisions for a specific child should always be made by the treating clinician, who can weigh vital signs, ongoing losses, and the full clinical picture.

Frequently Asked Questions

How is estimated blood volume (EBV) calculated in children?
EBV is calculated as body weight in kilograms multiplied by an age-based blood volume factor: about 100 mL/kg for premature infants, 90 mL/kg for full-term neonates, 80 mL/kg for infants up to one year, 75 mL/kg for children, and 70 mL/kg for adolescents and adults.
What is allowable blood loss and how is it calculated?
Allowable blood loss (ABL) estimates how much blood volume can be lost before hematocrit falls to a chosen target. It is calculated as EBV multiplied by (starting hematocrit minus target hematocrit) divided by starting hematocrit, assuming lost blood is replaced with a fluid that does not itself carry red cells.
Can this calculator be used to make transfusion decisions?
No. This tool provides an educational estimate only. Actual transfusion decisions depend on the child's vital signs, ongoing blood loss, comorbidities, and clinical trend, and must be made by the treating clinician.

Related calculators