Estimates how much blood can be lost, with the volume replaced, before the hemoglobin or hematocrit falls to a chosen lowest value.
Result
Enter the weight, choose the blood volume and enter the starting and lowest acceptable values.
Sources
3 studies
3
studies
1,159
citations
33
PubMed papers
Evidence
Known limitations
Gross corrected the allowable blood loss for dilution during replacement; the version quoted from his paper divides by the average hematocrit and gives a larger allowance than the simple formula.
Anesthesiology: Journal Metrics Score 2.6, Q1 · cited 1,159 times
A review of fluid and blood therapy in children that tabulates estimated blood volume by age (90–100 mL/kg preterm, 80–90 mL/kg from term to 3 months, 70 mL/kg in older children) and gives the MABL formula with hematocrit.
Indian J Anaesth: Journal Metrics Score 2.0, Q2 · cited 21 times
PubMed · Free full text · DOI
A teaching chapter for anesthesia students that works through allowable blood loss for a 60 kg woman with hematocrit values.
In: Ehrenfeld JM, Urman RD, Segal S, eds. Anesthesia Student Survival Guide. Springer · cited 4 times
The key paper has been cited 1,159 times, and 33 PubMed articles mention the allowable blood loss in their title or abstract. Citation counts from OpenAlex and article counts from PubMed, retrieved November 12, 2026. Journal Metrics Scores and quartiles are from this site’s current release; follow the journal name for details.
After the result
Before surgery · During bleeding · Any result
Plan for the expected loss. Measure, do not only estimate. The allowance is an estimate.
Next steps
Avoid common errors
4 common errors to avoid
and 2 more
When the estimate misleads
1Blood volume estimate
The mL/kg figures are population averages. Blood volume per kilogram of actual weight is lower in obesity and higher in pregnancy and in neonates.
2Assumes volume replacement
The formula assumes the circulating volume is kept constant while blood is lost. Without replacement, the hemoglobin falls later and the patient is hypovolemic instead.
3Hemoglobin lags behind bleeding
In fast bleeding the measured hemoglobin falls only as fluid is given; a normal value early on does not mean little blood was lost.
4Not a transfusion trigger
The lowest acceptable value is chosen by the team for the patient; the formula does not decide when to transfuse.
Formula
MABL = estimated blood volume × (starting − lowest acceptable hemoglobin or hematocrit) / starting; blood volume = weight × mL/kg.
EBV × (Hi − Hf) / Hi
MABL = estimated blood volume × (starting − lowest acceptable hemoglobin or hematocrit) / starting; blood volume = weight × mL/kg.
Formula and blood volumes
| Value | Formula |
|---|---|
| Estimated blood volume (mL) | weight (kg) × blood volume (mL/kg) from the table below |
| Maximum allowable blood loss (mL) | EBV × (starting − lowest acceptable) / starting, with hemoglobin or hematocrit in the same unit |
| Gross 1983, for comparison | EBV × (starting − lowest acceptable) / average of the two |
| Group | mL/kg |
|---|---|
| Preterm neonate | 95 |
| Term neonate | 85 |
| Infant (to 1 year) | 80 |
| Child (over 1 year) | 70 |
| Adult man | 75 |
| Adult woman | 65 |
Typical values from anesthesia teaching; published tables differ by about 5 to 10 mL/kg. Blood volume per kilogram of actual weight is lower in obesity and higher in pregnancy.
Gross 1983
Same measure
Neonates
Test cases
3 published cases, each also a test case
3 published cases; the calculator reproduces every result.
Worked examples
A pregnant woman at 40 weeks with acute transverse myelitis weighed 66 kg and had a hemoglobin of 12.4 g/dL before an emergency cesarean section. The report gives a maximum allowable blood loss of 830 mL against an estimated loss of about 600 mL.
“against the maximum allowable blood loss of 830 mL”
The report gives only the result; it does not state the blood volume per kilogram or the lowest acceptable hemoglobin, so these inputs are our reconstruction, not the authors’ method. 65 mL/kg and 10 g/dL give 830 mL to the nearest 10 mL, but other combinations do too (hematocrit 38% to 30% at 60 mL/kg gives 834 mL). At term, blood volume is roughly 40 to 50% above the non-pregnant value, so 65 mL/kg understates the allowance and is not a suitable figure for a pregnant patient.
Entered as: Body weight: 66 kg; Blood volume: Adult woman (65 mL/kg); Starting hemoglobin or hematocrit: 12.4 g/dL (hemoglobin); Lowest acceptable value: 10 g/dL (hemoglobin).
Source: Shekhar S et al., Cureus 2022 (PubMed · Free full text · DOI)
An anesthesia textbook chapter works through a young woman of 60 kg with an estimated blood volume of 65 mL/kg, a starting hematocrit of 36% and an acceptable nadir of 21%, roughly a hemoglobin of 7 g/dL.
“ABL = 4 L*(36-21)/36 = 1.7 L”
The chapter rounds the blood volume of 3,900 mL up to 4 L, which gives its 1.7 L; with 3,900 mL the allowance is 1,625 mL.
Entered as: Body weight: 60 kg; Blood volume: Adult woman (65 mL/kg); Starting hemoglobin or hematocrit: 36 % (hematocrit); Lowest acceptable value: 21 % (hematocrit).
Source: Dillon FX, In: Ehrenfeld JM, Urman RD, Segal S, eds. Anesthesia Student Survival Guide. Springer 2010 (Free full text · DOI)
In a study of 100 neonates having surgery, the authors calculated each baby’s maximum allowable blood loss with a blood volume of 90 mL/kg for term neonates and a target hemoglobin of 13 g/dL. The babies weighed 2.47 kg on average, with a starting hemoglobin of 15 g/dL.
“estimated blood volume (90 mL/kg for term neonate), HO is starting hemoglobin, and HI is target hemoglobin (13 g for neonates)”
A worked example from the study’s average baby, using the authors’ 90 mL/kg instead of the calculator’s 85. Their mean calculated allowance across babies was 28.6 mL, and the average blood loss 25.9 mL; in small babies a few milliliters matter.
Entered as: Body weight: 2.47 kg; Blood volume: Other (enter mL/kg); Blood volume per kg: 90 mL/kg; Starting hemoglobin or hematocrit: 15 g/dL (hemoglobin); Lowest acceptable value: 13 g/dL (hemoglobin).
Source: Tandale SR et al., Saudi J Anaesth 2019 (PubMed · Free full text · DOI)
FAQ
6 questions and answers
and 4 more answers
Questions
MABL = estimated blood volume × (starting hemoglobin − lowest acceptable hemoglobin) / starting hemoglobin. The blood volume is weight times a volume per kilogram, such as 65 mL/kg for an adult woman. A 70 kg man (75 mL/kg, 5,250 mL) with a hemoglobin of 14 g/dL and a lowest acceptable value of 8 g/dL has a MABL of 5,250 × 6 / 14 = 2,250 mL.
Yes. The formula uses a ratio, so it works with hemoglobin or hematocrit, as long as the starting and lowest acceptable values use the same measure. The calculator lets you choose hemoglobin in g/dL or g/L, or hematocrit in %.
Common values are about 95 mL/kg for preterm neonates, 85 mL/kg for term neonates, 80 mL/kg for infants, 70 mL/kg for children, 75 mL/kg for adult men and 65 mL/kg for adult women. Published tables differ by 5 to 10 mL/kg; studies sometimes use 90 mL/kg for term neonates or 70 mL/kg for adult men. Choose "Other" to enter your own value.
The simple formula divides by the starting value. Gross (1983) corrected for the fact that, as blood is lost and replaced, the blood lost later is more dilute; his version, as widely quoted, divides by the average of the starting and lowest values. Gross’s version gives a larger allowance; the calculator shows both in the working.
It is a clinical decision for the individual patient. It depends on age, heart and lung disease, ongoing bleeding and the type of surgery, and on local transfusion guidance. Some patients, such as preterm or unwell neonates and some patients with heart disease, may be managed with a higher value.
No. MABL is the estimated loss, with the volume replaced, before the hemoglobin or hematocrit reaches the chosen lowest value. It does not say whether or how much to transfuse. Estimated blood loss in theatre is often inaccurate, so the hemoglobin or hematocrit should be measured during major bleeding.
Further reading
5 references with PubMed and DOI links
5
references
4
free full text
From Gross JB, Anesthesiology 1983 to the newest case reports.
References
Contributed by Dr. Meng Zhao (MD · Former Neurosurgeon · Medical AI Researcher), from the original publications listed here. Last updated November 12, 2026. LinkedIn
The calculator code is tested against every worked example on this page before each release.
This calculator supports, and does not replace, clinical judgment. It is meant for healthcare professionals and is not medical advice for patients. Report an error through the contact page.
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Devine ideal body weight and adjusted weight from height and sex.
For weight estimates in obesity.
Another weight-based fluid estimate.
Which published Gross’s correction for dilution, with its current metrics.