Enter the packed cell volume (PCV) and hemoglobin (Hb) values into the calculator to determine the missing variable based on the PCV to Hb ratio.

PCV to Hb Ratio Calculator

Pick a direction, enter one value.

PCV → Hb
Hb → PCV
%
g/dL ▾
Ratio: 3 (tap to change)
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Standard rule of three: PCV ≈ Hb × 3. Change only if instructed.
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Medical disclaimer: This calculator provides a rough estimate for educational purposes only and does not diagnose anemia, polycythemia, or any condition. For interpretation of CBC/hematology results (or if you have concerning symptoms such as chest pain, shortness of breath, fainting, severe fatigue, or heavy bleeding), consult a licensed clinician or seek urgent care.

PCV to Hb Ratio Formula

The following formula is used to calculate the packed cell volume (PCV) or hemoglobin (Hb) based on the PCV to Hb ratio.

PCV = Hb * R

Variables:

  • PCV is the packed cell volume (hematocrit)
  • Hb is the hemoglobin level
  • R is the ratio (often approximated as 3 in the common “rule of 3”)

To estimate the packed cell volume (PCV), multiply the hemoglobin (Hb) level by the ratio (R). Many references teach a rough “rule of 3” (PCV ≈ 3 × Hb when Hb is in g/dL and PCV is in %), but the relationship is not exact and can vary between individuals and situations.

What is the PCV to Hb Ratio?

The PCV to Hb ratio describes the relationship between packed cell volume (PCV/hematocrit) and hemoglobin (Hb). A commonly taught approximation is that PCV (as a %) is about three times the Hb value (in g/dL). This is best thought of as a rough consistency check or quick estimate—not a diagnostic or monitoring tool—and lab results should be interpreted in clinical context.

Limitations of the “PCV ≈ 3 × Hb” Rule

This approximation may be inaccurate in many common situations. Examples include:

  • iron deficiency or other causes of microcytosis
  • macrocytosis (for example, B12/folate deficiency)
  • dehydration or overhydration
  • pregnancy
  • hemoglobinopathies (such as sickle cell disease or thalassemia)
  • recent bleeding, transfusion, or rapidly changing blood counts
  • differences in lab methods and reporting units (g/dL vs g/L; % vs L/L)

How to Calculate PCV to Hb Ratio?

The following steps outline how to calculate the PCV to Hb ratio.

  1. First, determine the hemoglobin (Hb) level (confirm the unit, such as g/dL).
  2. Next, determine the packed cell volume (PCV/hematocrit) (confirm the unit, such as %).
  3. If estimating PCV from Hb, use PCV = Hb × R (often R ≈ 3).
  4. If estimating Hb from PCV, use Hb = PCV ÷ R.
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Hemoglobin (Hb) level = 12 g/dL

Ratio (R) = 3

Using the formula PCV = Hb * R, the packed cell volume (PCV) would be 12 * 3 = 36%.