Plasma Volume Calculator

Estimate plasma volume from body weight, sex, and hematocrit using the Kaplan-Hakim formula, plus the derived total blood volume and plasma volume per kilogram.

Quick Facts

Formula
Kaplan-Hakim estimated plasma volume
EPV = (1 - Hct) x [a + (b x weight in kg)], with sex-specific a and b coefficients.
Typical range
~30-45 mL of plasma per kg
About 4-5% of body weight, roughly 55% of total blood volume.
Common use
Sizing therapeutic plasma exchange (TPE)
Clinicians use estimated plasma volume to plan single-volume or multi-volume exchanges.

Your Results

Calculated
Estimated plasma volume
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Kaplan-Hakim formula, mL
Plasma volume
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Same result in liters
Estimated total blood volume
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Plasma volume ÷ (1 - Hct)
Plasma volume per kg
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mL of plasma per kg body weight

Ready

Enter sex, body weight, and hematocrit, then calculate estimated plasma volume.

About the Plasma Volume Calculator

Plasma is the liquid, cell-free portion of blood that carries proteins, clotting factors, electrolytes, and cells in suspension. This calculator estimates plasma volume from body weight, sex, and hematocrit using the Kaplan-Hakim formula, a widely cited method for estimating plasma volume without a direct tracer study.

The Kaplan-Hakim formula

Estimated plasma volume (EPV) is calculated as:

  • Men: EPV (mL) = (1 - Hct) x [1530 + (41.0 x body weight in kg)]
  • Women: EPV (mL) = (1 - Hct) x [864 + (47.9 x body weight in kg)]

Hematocrit (Hct) is the fraction of blood volume occupied by red blood cells, entered here as a percentage and converted to a decimal before use. The bracketed term is a sex-specific estimate of total blood volume built from body weight; multiplying by (1 - Hct) removes the red-cell fraction and leaves the plasma fraction. Dividing the plasma volume back by (1 - Hct) recovers the estimated total blood volume, and dividing by body weight gives plasma volume per kilogram, a useful way to compare results across different body sizes.

Putting the result in context

Adult plasma volume typically runs about 30 to 45 mL per kilogram of body weight, roughly 4 to 5% of total body weight and about 55% of total blood volume. These are population averages built into the formula's coefficients; an individual's true plasma volume can differ due to hydration status, pregnancy, illness, or body composition that the formula does not capture directly. The Kaplan-Hakim estimate is commonly used to size therapeutic plasma exchange (TPE) procedures and to contextualize lab and fluid-balance figures, but it is not a substitute for a directly measured plasma volume, which requires an indicator-dilution technique such as radiolabeled albumin.

When to consult a professional

This tool performs the standard Kaplan-Hakim arithmetic for education and planning. It is not a diagnosis and should not be used alone to size a medical procedure or guide treatment. Any clinical decision, including plasma exchange volumes, should be confirmed by a licensed healthcare provider using the patient's full clinical picture.

Frequently Asked Questions

What formula does this Plasma Volume Calculator use?
It uses the Kaplan-Hakim formula for estimated plasma volume (EPV): EPV = (1 - hematocrit) x [a + (b x body weight in kg)], with a = 1530 and b = 41.0 for men, and a = 864 and b = 47.9 for women. Hematocrit is entered as a percentage and converted to a decimal fraction before use.
What is a typical plasma volume for an adult?
Adult plasma volume is roughly 30 to 45 mL per kg of body weight, or about 4 to 5% of total body weight, which corresponds to roughly 55% of total blood volume once red cells are excluded. These are population averages, not a target for any one person.
Why does hematocrit affect the plasma volume estimate?
Whole blood is made of plasma plus cellular components, mostly red blood cells. Hematocrit is the fraction of blood volume made up of red cells, so multiplying total blood volume by (1 - hematocrit) removes the cellular fraction and leaves the plasma fraction. A higher hematocrit means a smaller plasma share of the same blood volume.
How is an estimated plasma volume used clinically?
Estimated plasma volume is commonly used to size the exchange volume for therapeutic plasma exchange (TPE) and to put lab or fluid-balance numbers in context. It is a population-based estimate from weight, sex, and hematocrit, not a direct measurement; clinical measurement uses indicator-dilution techniques such as radiolabeled albumin. A clinician should confirm any figure used for treatment planning.

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