This tool is provided for education and reference only. It implements published formulas using the values you enter. It has no knowledge of your patient.
Estimated blood volume and allowable blood loss are approximations. They assume normovolemia and steady-state conditions that frequently do not hold in the operating room, and they do not account for ongoing resuscitation, third-space losses, coagulopathy, cardiac reserve, or any other patient-specific factor.
Output from this tool is not a recommendation, a transfusion trigger, or medical advice. Verify every number independently. Responsibility for patient care decisions rests entirely with the treating licensed clinician.
Estimated blood volume and allowable blood loss in millilitres, from weight, patient type, and starting versus lowest acceptable hematocrit or hemoglobin.
Standard — EBV × (Hi − Hf) ÷ Hi. The more conservative of the two, and the one most commonly quoted in textbooks and on board examinations.
Gross average — EBV × (Hi − Hf) ÷ Hav, where Hav is the mean of the starting and lowest acceptable values. Accounts for the fact that blood lost late in the case is already dilute, so it yields a larger allowance.
Both appear in the literature and both are taught. The standard form assumes every millilitre lost carries the starting hematocrit, which is true only at the first drop and increasingly wrong thereafter — so it under-estimates the true allowance and errs toward transfusing sooner. Gross's equation uses the average hematocrit over the period of loss and is closer to what actually happens during haemodilution, so it gives a larger number.
The gap between them widens as the target drops. Neither is a transfusion trigger. Both are starting points for a decision that also takes in rate of loss, cardiac reserve, ongoing surgical bleeding, and the patient in front of you.
| Patient | mL/kg |
|---|---|
| Premature neonate | 95 |
| Full-term neonate | 85 |
| Infant, 1–12 months | 80 |
| Child, 1–12 years | 75 |
| Adult male | 75 |
| Adult female | 65 |
Conventional teaching values. Sources differ by a few mL/kg, particularly for children and for the obese patient, where lean body weight is generally the better basis.