Allowable Blood Loss Calculator
Estimate maximum allowable blood loss from weight and hematocrit, a surgical planning figure.
Awaiting Data
Enter your details and tap Calculate to see your results appear here.
Your result appears here.
What it measures
Allowable blood loss is the volume a patient can lose before reaching a chosen lowest safe hematocrit. Surgical teams estimate it ahead of an operation to plan fluids and transfusion. It rests on body weight, a blood volume factor, and two hematocrit values.
This tool gives a planning estimate only. Real care depends on the patient, the procedure, and clinical judgement. For the volume side, see our Blood Volume Calculator.
How to use this calculator
- Pick the patient type for the blood volume factor.
- Enter body weight.
- Enter the starting and lowest safe hematocrit.
- Tap Calculate for the allowable loss.
The formula used
Allowable loss = EBV × (initial Hct − lowest Hct) / initial Hct
- EBV
- Estimated blood volume.
- factor
- Millilitres of blood per kg by patient type.
- Hct
- Hematocrit, the red cell share of blood.
Understanding Your Results
Tips to Improve
- Confirm the blood volume factor for your patient.
- Set the safe floor with the care team.
- Re estimate as the case changes.
- Never use this in place of clinical monitoring.
Frequently Asked Questions
Many plans use around 30 percent, though it varies by patient and case.
Yes. Blood per kilogram differs across adults, children, and infants.
No. It is a planning estimate, not a live measurement.
Scientific References
- Gross, J. B. (1983). Estimating allowable blood loss. Anesthesiology, 58(3), 277–280.
- Miller, R. D. (2014). Miller's Anesthesia (8th ed.).