Plasma is the liquid part of blood, about 55% of blood volume. Plasma volume estimates guide therapeutic plasma exchange (usually 1–1.5 plasma volumes per session).
How to use the Plasma Volume Calculator
- Sex
- Weight
- Haematocrit
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter sex, weight and haematocrit.
Inputs explained
| Field | What to enter |
|---|---|
| Sex | Choose one: Male, Female |
| Weight | Units: kg, lb, st, g |
| Haematocrit | In % |
What each result means
- Plasma volume (70 mL/kg) = 70×[Weight]×(1 – [Haematocrit]÷100)
- 1.25 plasma volumes (typical exchange) = [Plasma volume (Kaplan)]×1.25
Example values
How the main result changes when Weight changes and everything else stays at the example values above:
| Weight (kg) | Plasma volume (Kaplan) (mL) |
|---|---|
| 37.5 | 1,779 |
| 56.25 | 2,225 |
| 75 | 2,671 |
| 93.75 | 3,117 |
| 112.5 | 3,563 |
| 150 | 4,454 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Kaplan: PV (mL) = (1 − Hct) × (b + c × weight kg); men b = 1530, c = 41; women b = 864, c = 47.9
Simple: PV = 70 mL/kg × weight × (1 − Hct)
Worked example
Inputs — Sex: Male; Weight: 75 kg; Haematocrit: 42 %.
Results — Plasma volume (Kaplan) = 2,671 mL; Plasma volume (70 mL/kg) = 3,045 mL; 1.25 plasma volumes (typical exchange) = 3,339 mL.
Key terms
- Plasma exchange
- Removing plasma and replacing it with albumin or donor plasma.
Frequently asked questions
What is a normal plasma volume?
About 40–50 mL per kg, roughly 2.5–3.5 litres in adults.
How much plasma is exchanged in plasmapheresis?
Usually 1–1.5 plasma volumes per session.
Why does haematocrit matter?
The higher the haematocrit, the smaller the plasma share of blood.