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Allowable Blood Loss Calculator

Work out allowable blood loss instantly with clear inputs, formula shown and shareable results.

About Allowable Blood Loss Calculator

Calculates how much blood can be lost before the haematocrit falls to the chosen transfusion trigger, using estimated blood volume.

Formula

Allowable blood loss

ABL = EBV x (starting Hct - minimum acceptable Hct) / starting Hct, with EBV = weight x mL/kg

Worked example

With the default values below, Allowable Blood Loss Calculator returns Maximum allowable blood loss of 1,400. Change any input above and every figure here is recalculated in your browser.

Inputs used

Body weightaccepts 2–250 kg
70 kg
Blood volume per kilogramaccepts 50–100 mL/kg
70 mL/kg
Starting haematocritaccepts 15–60 %
42 %
Lowest acceptable haematocritaccepts 15–45 %
30 %

Results

Maximum allowable blood loss
1,400 mL
Estimated blood volume
4,900 mL
Loss expressed in 280 mL units
5.00

Step by step

  1. 1Values used
  2. 2Allowable blood loss
  3. 3Maximum allowable blood loss= 1,400 mL
  4. 4Estimated blood volume= 4,900 mL
  5. 5Loss expressed in 280 mL units= 5.00

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

What trigger should be used?

Restrictive thresholds around a haemoglobin of 70 to 80 g/L are standard in stable patients; cardiac disease may warrant higher.

Does crystalloid replacement change this?

Yes. Dilution lowers haematocrit without further red cell loss, so the calculation assumes normovolaemia.

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