Hematocrit / Hemoglobin Ratio Calculator

The Rule of 3

In healthy individuals with normal red cell indices, hematocrit (expressed as a percentage) should equal roughly three times the hemoglobin concentration (g/dL). Conversely, RBC count (millions/μL) × 3 ≈ HGB, and HGB × 3 ≈ HCT. This "Rule of 3" is a quick laboratory consistency check used in CBC verification.

Causes of Deviation

• HCT > 3 × HGB — Microcytic anemia (iron deficiency, thalassemia), hyperglycemia in MCH-based analyzers
• HCT < 3 × HGB — Macrocytic anemia (B12/folate deficiency), lipemia, high WBC count, cold agglutinins
• Spurious results: hemolysis, paraproteins, severe leukocytosis

Normal Reference Ranges

• Hemoglobin: Men 13.5–17.5 g/dL; Women 12.0–15.5 g/dL
• Hematocrit: Men 38.8–50%; Women 34.9–44.5%