The Red Cell Distribution Width (RDW) Calculator measures the variation in size of your red blood cells (RBCs). It helps diagnose different types of anemia and other blood disorders by analyzing RBC size differences.
Definition
Red Cell Distribution Width (RDW) is a blood test parameter that quantifies the degree of variation in red blood cell volume (anisocytosis). It is reported as a percentage or coefficient of variation (CV).
Purpose
- Differentiates between types of anemia (iron deficiency, B12/folate deficiency, thalassemia)
- Helps monitor chronic diseases affecting RBC production
- Used alongside MCV for comprehensive anemia classification
Formula:
RDW (%) = Standard Deviation of RBC Volume Mean Corpuscular Volume × 100
How to Use the RDW Calculator
- Input the standard deviation of RBC volume (from CBC report)
- Enter the Mean Corpuscular Volume (MCV) in fL
- Click Calculate to get RDW percentage
Example Calculation
- SD of RBC volume = 12.5 fL
- MCV = 85 fL
12.5
85
🧮 RDW (Red Cell Distribution Width) Calculator
📐 Formula:
RDW (%) =
Standard Deviation of RBC Volume
Mean Corpuscular Volume
× 100
Normal RDW Values
- Adults: 11.5% to 14.5%
- Newborns: Slightly higher (up to 15.5%)
Clinical Interpretation
| RDW Result | Possible Conditions |
|---|---|
| High RDW (>14.5%) | Iron deficiency anemia, B12/folate deficiency, hemolytic anemia |
| Normal RDW | Thalassemia, chronic disease anemia (if MCV is abnormal) |
| Low RDW | Less clinically significant (may occur in microcytic anemia) |
Limitations
- Must be interpreted with MCV and other CBC parameters
- Not diagnostic alone – requires correlation with clinical findings
- Some automated analyzers may report slightly different reference ranges
Use our RDW Calculator to better understand your complete blood count results!
